24 Ranges library [ranges]

24.1 General [ranges.general]

This Clause describes components for dealing with ranges of elements.

The following subclauses describe range and view requirements, and components for range primitives as summarized in Table 90 .

Table 90: Ranges library summary [tab:range.summary]

🔗		Subclause	Header
🔗	[range.access]	Range access	<ranges>
🔗	[range.req]	Requirements
🔗	[range.utility]	Range utilities
🔗	[range.factories]	Range factories
🔗	[range.adaptors]	Range adaptors

24.2 Header <ranges> synopsis [ranges.syn]

🔗

#include <compare> // see [compare.syn] #include <initializer_list> // see [initializer.list.syn] #include <iterator> // see [iterator.synopsis] namespace std::ranges { inline namespace unspecified { // [range.access], range access inline constexpr unspecified begin = unspecified; inline constexpr unspecified end = unspecified; inline constexpr unspecified cbegin = unspecified; inline constexpr unspecified cend = unspecified; inline constexpr unspecified rbegin = unspecified; inline constexpr unspecified rend = unspecified; inline constexpr unspecified crbegin = unspecified; inline constexpr unspecified crend = unspecified; inline constexpr unspecified size = unspecified; inline constexpr unspecified ssize = unspecified; inline constexpr unspecified empty = unspecified; inline constexpr unspecified data = unspecified; inline constexpr unspecified cdata = unspecified; } // [range.range], ranges template<class T> concept range = see below; template<class T> inline constexpr bool enable_borrowed_range = false; template<class T> concept borrowed_range = see below; template<class T> using iterator_t = decltype(ranges::begin(declval<T&>())); template<range R> using sentinel_t = decltype(ranges::end(declval<R&>())); template<range R> using range_difference_t = iter_difference_t<iterator_t<R>>; template<sized_range R> using range_size_t = decltype(ranges::size(declval<R&>())); template<range R> using range_value_t = iter_value_t<iterator_t<R>>; template<range R> using range_reference_t = iter_reference_t<iterator_t<R>>; template<range R> using range_rvalue_reference_t = iter_rvalue_reference_t<iterator_t<R>>; // [range.sized], sized ranges template<class> inline constexpr bool disable_sized_range = false; template<class T> concept sized_range = see below; // [range.view], views template<class T> inline constexpr bool enable_view = see below; struct view_base { }; template<class T> concept view = see below; // [range.refinements], other range refinements template<class R, class T> concept output_range = see below; template<class T> concept input_range = see below; template<class T> concept forward_range = see below; template<class T> concept bidirectional_range = see below; template<class T> concept random_access_range = see below; template<class T> concept contiguous_range = see below; template<class T> concept common_range = see below; template<class T> concept viewable_range = see below; // [view.interface], class template view_interface template<class D> requires is_class_v<D> && same_as<D, remove_cv_t<D>> class view_interface; // [range.subrange], sub-ranges enum class subrange_kind : bool { unsized, sized }; template<input_or_output_iterator I, sentinel_for S = I, subrange_kind K = see below> requires (K == subrange_kind::sized || !sized_sentinel_for<S, I>) class subrange; template<class I, class S, subrange_kind K> inline constexpr bool enable_borrowed_range<subrange<I, S, K>> = true; // [range.dangling], dangling iterator handling struct dangling; template<range R> using borrowed_iterator_t = see below; template<range R> using borrowed_subrange_t = see below; // [range.empty], empty view template<class T> requires is_object_v<T> class empty_view; template<class T> inline constexpr bool enable_borrowed_range<empty_view<T>> = true; namespace views { template<class T> inline constexpr empty_view<T> empty{}; } // [range.single], single view template<copy_constructible T> requires is_object_v<T> class single_view; namespace views { inline constexpr unspecified single = unspecified; } template<bool Const, class T> using maybe-const = conditional_t<Const, const T, T>; // exposition only // [range.iota], iota view template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t> requires weakly-equality-comparable-with<W, Bound> && copyable<W> class iota_view; template<class W, class Bound> inline constexpr bool enable_borrowed_range<iota_view<W, Bound>> = true; namespace views { inline constexpr unspecified iota = unspecified; } // [range.istream], istream view template<movable Val, class CharT, class Traits = char_traits<CharT>> requires see below class basic_istream_view; template<class Val, class CharT, class Traits> basic_istream_view<Val, CharT, Traits> istream_view(basic_istream<CharT, Traits>& s); // [range.all], all view namespace views { inline constexpr unspecified all = unspecified; template<viewable_range R> using all_t = decltype(all(declval<R>())); } template<range R> requires is_object_v<R> class ref_view; template<class T> inline constexpr bool enable_borrowed_range<ref_view<T>> = true; // [range.filter], filter view template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class filter_view; namespace views { inline constexpr unspecified filter = unspecified; } // [range.transform], transform view template<input_range V, copy_constructible F> requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> && can-reference<invoke_result_t<F&, range_reference_t<V>>> class transform_view; namespace views { inline constexpr unspecified transform = unspecified; } // [range.take], take view template<view> class take_view; template<class T> inline constexpr bool enable_borrowed_range<take_view<T>> = enable_borrowed_range<T>; namespace views { inline constexpr unspecified take = unspecified; } // [range.take.while], take while view template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> class take_while_view; namespace views { inline constexpr unspecified take_while = unspecified; } // [range.drop], drop view template<view V> class drop_view; template<class T> inline constexpr bool enable_borrowed_range<drop_view<T>> = enable_borrowed_range<T>; namespace views { inline constexpr unspecified drop = unspecified; } // [range.drop.while], drop while view template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> class drop_while_view; template<class T, class Pred> inline constexpr bool enable_borrowed_range<drop_while_view<T, Pred>> = enable_borrowed_range<T>; namespace views { inline constexpr unspecified drop_while = unspecified; } // [range.join], join view template<input_range V> requires view<V> && input_range<range_reference_t<V>> class join_view; namespace views { inline constexpr unspecified join = unspecified; } // [range.lazy.split], lazy split view template<class R> concept tiny-range = see below; // exposition only template<input_range V, forward_range Pattern> requires view<V> && view<Pattern> && indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> && (forward_range<V> || tiny-range<Pattern>) class lazy_split_view; // [range.split], split view template<forward_range V, forward_range Pattern> requires view<V> && view<Pattern> && indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> class split_view; namespace views { inline constexpr unspecified lazy_split = unspecified; inline constexpr unspecified split = unspecified; } // [range.counted], counted view namespace views { inline constexpr unspecified counted = unspecified; } // [range.common], common view template<view V> requires (!common_range<V> && copyable<iterator_t<V>>) class common_view; template<class T> inline constexpr bool enable_borrowed_range<common_view<T>> = enable_borrowed_range<T>; namespace views { inline constexpr unspecified common = unspecified; } // [range.reverse], reverse view template<view V> requires bidirectional_range<V> class reverse_view; template<class T> inline constexpr bool enable_borrowed_range<reverse_view<T>> = enable_borrowed_range<T>; namespace views { inline constexpr unspecified reverse = unspecified; } // [range.elements], elements view template<input_range V, size_t N> requires see below class elements_view; template<class T, size_t N> inline constexpr bool enable_borrowed_range<elements_view<T, N>> = enable_borrowed_range<T>; template<class R> using keys_view = elements_view<views::all_t<R>, 0>; template<class R> using values_view = elements_view<views::all_t<R>, 1>; namespace views { template<size_t N> inline constexpr unspecified elements = unspecified; inline constexpr auto keys = elements<0>; inline constexpr auto values = elements<1>; } } namespace std { namespace views = ranges::views; template<class T> struct tuple_size; template<size_t I, class T> struct tuple_element; template<class I, class S, ranges::subrange_kind K> struct tuple_size<ranges::subrange<I, S, K>> : integral_constant<size_t, 2> {}; template<class I, class S, ranges::subrange_kind K> struct tuple_element<0, ranges::subrange<I, S, K>> { using type = I; }; template<class I, class S, ranges::subrange_kind K> struct tuple_element<1, ranges::subrange<I, S, K>> { using type = S; }; template<class I, class S, ranges::subrange_kind K> struct tuple_element<0, const ranges::subrange<I, S, K>> { using type = I; }; template<class I, class S, ranges::subrange_kind K> struct tuple_element<1, const ranges::subrange<I, S, K>> { using type = S; }; }

Within this Clause, for an integer-like type X ([iterator.concept.winc]), make-unsigned-like-t<X> denotes make_unsigned_t<X> if X is an integer type; otherwise, it denotes a corresponding unspecified unsigned-integer-like type of the same width as X.

For an expression x of type X, to-unsigned-like(x) is x explicitly converted to make-unsigned-like-t<X>.

Also within this Clause, make-signed-like-t<X> for an integer-like type X denotes make_signed_t<X> if X is an integer type; otherwise, it denotes a corresponding unspecified signed-integer-like type of the same width as X.

24.3 Range access [range.access]

24.3.1 General [range.access.general]

In addition to being available via inclusion of the <ranges> header, the customization point objects in [range.access] are available when <iterator> is included.

Within [range.access], the reified object of a subexpression E denotes

(2.1)
the same object as E if E is a glvalue, or
(2.2)
the result of applying the temporary materialization conversion ([conv.rval]) to E otherwise.

24.3.2 ranges::begin [range.access.begin]

The name ranges::begin denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges::begin(E) is ill-formed.
(2.2)
Otherwise, if T is an array type ([basic.compound]) and remove_all_extents_t<T> is an incomplete type, ranges::begin(E) is ill-formed with no diagnostic required.
(2.3)
Otherwise, if T is an array type, ranges::begin(E) is expression-equivalent to t + 0.
(2.4)
Otherwise, if decay-copy(t.begin()) is a valid expression whose type models input_or_output_iterator, ranges::begin(E) is expression-equivalent to decay-copy(t.begin()).
(2.5)
Otherwise, if T is a class or enumeration type and decay-copy(begin(t)) is a valid expression whose type models input_or_output_iterator with overload resolution performed in a context in which unqualified lookup for begin finds only the declarations void begin(auto&) = delete; void begin(const auto&) = delete; then ranges::begin(E) is expression-equivalent to decay-copy(begin(t)) with overload resolution performed in the above context.
(2.6)
Otherwise, ranges::begin(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::begin(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::begin(E) is a valid expression, its type models input_or_output_iterator .

— end note]

24.3.3 ranges::end [range.access.end]

The name ranges::end denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges::end(E) is ill-formed.
(2.2)
Otherwise, if T is an array type ([basic.compound]) and remove_all_extents_t<T> is an incomplete type, ranges::end(E) is ill-formed with no diagnostic required.
(2.3)
Otherwise, if T is an array of unknown bound, ranges::end(E) is ill-formed.
(2.4)
Otherwise, if T is an array, ranges::end(E) is expression-equivalent to t + extent_v<T>.
(2.5)
Otherwise, if decay-copy(t.end()) is a valid expression whose type models sentinel_for<iterator_t<T>> then ranges::end(E) is expression-equivalent to decay-copy(t.end()).
(2.6)
Otherwise, if T is a class or enumeration type and decay-copy(end(t)) is a valid expression whose type models sentinel_for<iterator_t<T>> with overload resolution performed in a context in which unqualified lookup for end finds only the declarations void end(auto&) = delete; void end(const auto&) = delete; then ranges::end(E) is expression-equivalent to decay-copy(end(t)) with overload resolution performed in the above context.
(2.7)
Otherwise, ranges::end(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::end(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::end(E) is a valid expression, the types S and I of ranges::end(E) and ranges::begin(E) model sentinel_for<S, I>.

— end note]

24.3.4 ranges::cbegin [range.access.cbegin]

The name ranges::cbegin denotes a customization point object ([customization.point.object]).

The expression ranges::cbegin(E) for a subexpression E of type T is expression-equivalent to:

(1.1)
ranges::begin(static_cast<const T&>(E)) if E is an lvalue.
(1.2)
Otherwise, ranges::begin(static_cast<const T&&>(E)).

[Note 1:

Whenever ranges::cbegin(E) is a valid expression, its type models input_or_output_iterator .

— end note]

24.3.5 ranges::cend [range.access.cend]

The name ranges::cend denotes a customization point object ([customization.point.object]).

The expression ranges::cend(E) for a subexpression E of type T is expression-equivalent to:

(1.1)
ranges::end(static_cast<const T&>(E)) if E is an lvalue.
(1.2)
Otherwise, ranges::end(static_cast<const T&&>(E)).

[Note 1:

Whenever ranges::cend(E) is a valid expression, the types S and I of the expressions ranges::cend(E) and ranges::cbegin(E) model sentinel_for<S, I>.

— end note]

24.3.6 ranges::rbegin [range.access.rbegin]

The name ranges::rbegin denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges::rbegin(E) is ill-formed.
(2.2)
Otherwise, if T is an array type ([basic.compound]) and remove_all_extents_t<T> is an incomplete type, ranges::rbegin(E) is ill-formed with no diagnostic required.
(2.3)
Otherwise, if decay-copy(t.rbegin()) is a valid expression whose type models input_or_output_iterator, ranges::rbegin(E) is expression-equivalent to decay-copy(t.rbegin()).
(2.4)
Otherwise, if T is a class or enumeration type and decay-copy(rbegin(t)) is a valid expression whose type models input_or_output_iterator with overload resolution performed in a context in which unqualified lookup for rbegin finds only the declarations void rbegin(auto&) = delete; void rbegin(const auto&) = delete; then ranges::rbegin(E) is expression-equivalent to decay-copy(rbegin(t)) with overload resolution performed in the above context.
(2.5)
Otherwise, if both ranges::begin(t) and ranges::end(t) are valid expressions of the same type which models bidirectional_iterator ([iterator.concept.bidir]), ranges::rbegin(E) is expression-equivalent to make_reverse_iterator(ranges::end(t)).
(2.6)
Otherwise, ranges::rbegin(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::rbegin(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::rbegin(E) is a valid expression, its type models input_or_output_iterator .

— end note]

24.3.7 ranges::rend [range.access.rend]

The name ranges::rend denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges::rend(E) is ill-formed.
(2.2)
Otherwise, if T is an array type ([basic.compound]) and remove_all_extents_t<T> is an incomplete type, ranges::rend(E) is ill-formed with no diagnostic required.
(2.3)
Otherwise, if decay-copy(t.rend()) is a valid expression whose type models sentinel_for<decltype(ranges::rbegin(E))> then ranges::rend(E) is expression-equivalent to decay-copy(t.rend()).
(2.4)
Otherwise, if T is a class or enumeration type and decay-copy(rend(t)) is a valid expression whose type models sentinel_for<decltype(ranges::rbegin(E))> with overload resolution performed in a context in which unqualified lookup for rend finds only the declarations void rend(auto&) = delete; void rend(const auto&) = delete; then ranges::rend(E) is expression-equivalent to decay-copy(rend(t)) with overload resolution performed in the above context.
(2.5)
Otherwise, if both ranges::begin(t) and ranges::end(t) are valid expressions of the same type which models bidirectional_iterator ([iterator.concept.bidir]), then ranges::rend(E) is expression-equivalent to make_reverse_iterator(ranges::begin(t)).
(2.6)
Otherwise, ranges::rend(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::rend(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::rend(E) is a valid expression, the types S and I of the expressions ranges::rend(E) and ranges::rbegin(E) model sentinel_for<S, I>.

— end note]

24.3.8 ranges::crbegin [range.access.crbegin]

The name ranges::crbegin denotes a customization point object ([customization.point.object]).

The expression ranges::crbegin(E) for a subexpression E of type T is expression-equivalent to:

(1.1)
ranges::rbegin(static_cast<const T&>(E)) if E is an lvalue.
(1.2)
Otherwise, ranges::rbegin(static_cast<const T&&>(E)).

[Note 1:

Whenever ranges::crbegin(E) is a valid expression, its type models input_or_output_iterator .

— end note]

24.3.9 ranges::crend [range.access.crend]

The name ranges::crend denotes a customization point object ([customization.point.object]).

The expression ranges::crend(E) for a subexpression E of type T is expression-equivalent to:

(1.1)
ranges::rend(static_cast<const T&>(E)) if E is an lvalue.
(1.2)
Otherwise, ranges::rend(static_cast<const T&&>(E)).

[Note 1:

Whenever ranges::crend(E) is a valid expression, the types S and I of the expressions ranges::crend(E) and ranges::crbegin(E) model sentinel_for<S, I>.

— end note]

24.3.10 ranges::size [range.prim.size]

The name ranges::size denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If T is an array of unknown bound ([dcl.array]), ranges::size(E) is ill-formed.
(2.2)
Otherwise, if T is an array type, ranges::size(E) is expression-equivalent to decay-copy(extent_v<T>).
(2.3)
Otherwise, if disable_sized_range<remove_cv_t<T>> ([range.sized]) is false and decay-copy(t.size()) is a valid expression of integer-like type ([iterator.concept.winc]), ranges::size(E) is expression-equivalent to decay-copy(t.size()).
(2.4)
Otherwise, if T is a class or enumeration type, disable_sized_range<remove_cv_t<T>> is false and decay-copy(size(t)) is a valid expression of integer-like type with overload resolution performed in a context in which unqualified lookup for size finds only the declarations void size(auto&) = delete; void size(const auto&) = delete; then ranges::size(E) is expression-equivalent to decay-copy(size(t)) with overload resolution performed in the above context.
(2.5)
Otherwise, if to-unsigned-like(ranges::end(t) - ranges::begin(t)) ([ranges.syn]) is a valid expression and the types I and S of ranges::begin(t) and ranges::end(t) (respectively) model both sized_sentinel_for<S, I> ([iterator.concept.sizedsentinel]) and forward_iterator, then ranges::size(E) is expression-equivalent to to-unsigned-like(ranges::end(t) - ranges::begin(t)).
(2.6)
Otherwise, ranges::size(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::size(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::size(E) is a valid expression, its type is integer-like.

— end note]

24.3.11 ranges::ssize [range.prim.ssize]

The name ranges::ssize denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

If ranges::size(t) is ill-formed, ranges::ssize(E) is ill-formed.

Otherwise let D be make-signed-like-t<decltype(ranges::size(t))>, or ptrdiff_t if it is wider than that type; ranges::ssize(E) is expression-equivalent to static_cast<D>(ranges::size(t)).

24.3.12 ranges::empty [range.prim.empty]

The name ranges::empty denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If T is an array of unknown bound ([basic.compound]), ranges::empty(E) is ill-formed.
(2.2)
Otherwise, if bool(t.empty()) is a valid expression, ranges::empty(E) is expression-equivalent to bool(t.empty()).
(2.3)
Otherwise, if (ranges::size(t) == 0) is a valid expression, ranges::empty(E) is expression-equivalent to (ranges::size(t) == 0).
(2.4)
Otherwise, if bool(ranges::begin(t) == ranges::end(t)) is a valid expression and the type of ranges::begin(t) models forward_iterator, ranges::empty(E) is expression-equivalent to bool(ranges::begin(t) == ranges::end(t)).
(2.5)
Otherwise, ranges::empty(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::empty(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::empty(E) is a valid expression, it has type bool.

— end note]

24.3.13 ranges::data [range.prim.data]

The name ranges::data denotes a customization point object ([customization.point.object]).

Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.

Then:

(2.1)
If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges::data(E) is ill-formed.
(2.2)
Otherwise, if T is an array type ([basic.compound]) and remove_all_extents_t<T> is an incomplete type, ranges::data(E) is ill-formed with no diagnostic required.
(2.3)
Otherwise, if decay-copy(t.data()) is a valid expression of pointer to object type, ranges::data(E) is expression-equivalent to decay-copy(t.data()).
(2.4)
Otherwise, if ranges::begin(t) is a valid expression whose type models contiguous_iterator, ranges::data(E) is expression-equivalent to to_address(ranges::begin(t)).
(2.5)
Otherwise, ranges::data(E) is ill-formed.

[Note 1:

Diagnosable ill-formed cases above result in substitution failure when ranges::data(E) appears in the immediate context of a template instantiation.

— end note]

[Note 2:

Whenever ranges::data(E) is a valid expression, it has pointer to object type.

— end note]

24.3.14 ranges::cdata [range.prim.cdata]

The name ranges::cdata denotes a customization point object ([customization.point.object]).

The expression ranges::cdata(E) for a subexpression E of type T is expression-equivalent to:

(1.1)
ranges::data(static_cast<const T&>(E)) if E is an lvalue.
(1.2)
Otherwise, ranges::data(static_cast<const T&&>(E)).

[Note 1:

Whenever ranges::cdata(E) is a valid expression, it has pointer to object type.

— end note]

24.4 Range requirements [range.req]

24.4.1 General [range.req.general]

Ranges are an abstraction that allow a C++ program to operate on elements of data structures uniformly.

Calling ranges::begin on a range returns an object whose type models input_or_output_iterator ([iterator.concept.iterator]).

Calling ranges::end on a range returns an object whose type S, together with the type I of the object returned by ranges::begin, models sentinel_for<S, I>.

The library formalizes the interfaces, semantics, and complexity of ranges to enable algorithms and range adaptors that work efficiently on different types of sequences.

The range concept requires that ranges::begin and ranges::end return an iterator and a sentinel, respectively.

The sized_range concept refines range with the requirement that ranges::size be amortized

O (1)

The view concept specifies requirements on a range type with constant-time destruction and move operations.

Several refinements of range group requirements that arise frequently in concepts and algorithms.

Common ranges are ranges for which ranges::begin and ranges::end return objects of the same type.

Random access ranges are ranges for which ranges::begin returns a type that models random_access_iterator ([iterator.concept.random.access]).

(Contiguous, bidirectional, forward, input, and output ranges are defined similarly.)

Viewable ranges can be converted to views.

24.4.2 Ranges [range.range]

The range concept defines the requirements of a type that allows iteration over its elements by providing an iterator and sentinel that denote the elements of the range.

🔗

template<class T>
  concept range =
    requires(T& t) {
      ranges::begin(t);         // sometimes equality-preserving (see below)
      ranges::end(t);
    };

The required expressions ranges::begin(t) and ranges::end(t) of the range concept do not require implicit expression variations ([concepts.equality]).

Given an expression t such that decltype((t)) is T&, T models range only if

(3.1)
[ranges::begin(t), ranges::end(t)) denotes a range ([iterator.requirements.general]),
(3.2)
both ranges::begin(t) and ranges::end(t) are amortized constant time and non-modifying, and
(3.3)
if the type of ranges::begin(t) models forward_iterator, ranges::begin(t) is equality-preserving.

[Note 1:

Equality preservation of both ranges::begin and ranges::end enables passing a range whose iterator type models forward_iterator to multiple algorithms and making multiple passes over the range by repeated calls to ranges::begin and ranges::end.

Since ranges::begin is not required to be equality-preserving when the return type does not model forward_iterator, it is possible for repeated calls to not return equal values or to not be well-defined.

— end note]

🔗

template<class T>
  concept borrowed_range =
    range<T> && (is_lvalue_reference_v<T> || enable_borrowed_range<remove_cvref_t<T>>);

Given an expression E such that decltype((E)) is T, T models borrowed_range only if the validity of iterators obtained from the object denoted by E is not tied to the lifetime of that object.

[Note 2:

Since the validity of iterators is not tied to the lifetime of an object whose type models borrowed_range, a function can accept arguments of such a type by value and return iterators obtained from it without danger of dangling.

— end note]

🔗

template<class>
  inline constexpr bool enable_borrowed_range = false;

Remarks: Pursuant to [namespace.std], users may specialize enable_borrowed_range for cv-unqualified program-defined types.

Such specializations shall be usable in constant expressions ([expr.const]) and have type const bool.

[Example 1:

Each specialization S of class template subrange ([range.subrange]) models borrowed_range because

(8.1)
enable_borrowed_range<S> is specialized to have the value true, and
(8.2)
S's iterators do not have validity tied to the lifetime of an S object because they are “borrowed” from some other range.

— end example]

24.4.3 Sized ranges [range.sized]

The sized_range concept refines range with the requirement that the number of elements in the range can be determined in amortized constant time using ranges::size.

🔗

template<class T>
  concept sized_range =
    range<T> && requires(T& t) { ranges::size(t); };

Given an lvalue t of type remove_reference_t<T>, T models sized_range only if

(2.1)
ranges::size(t) is amortized $O (1)$ , does not modify t, and is equal to ranges::distance(t), and
(2.2)
if iterator_t<T> models forward_iterator, ranges::size(t) is well-defined regardless of the evaluation of ranges::begin(t).
[Note 1:
ranges::size(t) is otherwise not required to be well-defined after evaluating ranges::begin(t).

For example, it is possible for ranges::size(t) to be well-defined for a sized_range whose iterator type does not model forward_iterator only if evaluated before the first call to ranges::begin(t).
— end note]

🔗

template<class>
  inline constexpr bool disable_sized_range = false;

Remarks: Pursuant to [namespace.std], users may specialize disable_sized_range for cv-unqualified program-defined types.

Such specializations shall be usable in constant expressions ([expr.const]) and have type const bool.

[Note 2:

disable_sized_range allows use of range types with the library that satisfy but do not in fact model sized_range .

— end note]

24.4.4 Views [range.view]

The view concept specifies the requirements of a range type that has constant time move construction, move assignment, and destruction; that is, the cost of these operations is independent of the number of elements in the view .

🔗

template<class T>
  concept view =
    range<T> && movable<T> && enable_view<T>;

T models view only if:

(2.1)
T has $O (1)$ move construction; and
(2.2)
T has $O (1)$ move assignment; and
(2.3)
T has $O (1)$ destruction; and
(2.4)
copy_constructible<T> is false, or T has $O (1)$ copy construction; and
(2.5)
copyable<T> is false, or T has $O (1)$ copy assignment.

[Example 1:

Examples of views are:

(3.1)
A range type that wraps a pair of iterators.
(3.2)
A range type that holds its elements by shared_ptr and shares ownership with all its copies.
(3.3)
A range type that generates its elements on demand.

Most containers are not views since destruction of the container destroys the elements, which cannot be done in constant time.

— end example]

Since the difference between range and view is largely semantic, the two are differentiated with the help of enable_view.

🔗

template<class T>
  inline constexpr bool is-derived-from-view-interface = see below;     // exposition only
template<class T>
  inline constexpr bool enable_view =
    derived_from<T, view_base> || is-derived-from-view-interface<T>;

For a type T, is-derived-from-view-interface<T> is true if and only if T has exactly one public base class view_interface for some type U and T has no base classes of type view_interface<V> for any other type V.

Remarks: Pursuant to [namespace.std], users may specialize enable_view to true for cv-unqualified program-defined types which model view, and false for types which do not.

Such specializations shall be usable in constant expressions ([expr.const]) and have type const bool.

24.5 Range utilities [range.utility]

24.5.1 General [range.utility.general]

The components in [range.utility] are general utilities for representing and manipulating ranges.

24.5.2 Helper concepts [range.utility.helpers]

Many of the types in subclause [range.utility] are specified in terms of the following exposition-only concepts: template<class R> concept simple-view = // exposition only view<R> && range<const R> && same_as<iterator_t<R>, iterator_t<const R>> && same_as<sentinel_t<R>, sentinel_t<const R>>; template<class I> concept has-arrow = // exposition only input_iterator && (is_pointer_v || requires(I i) { i.operator->(); }); template<class T, class U> concept different-from = // exposition only !same_as<remove_cvref_t<T>, remove_cvref_t>;

24.5.3 View interface [view.interface]

24.5.3.1 General [view.interface.general]

The class template view_interface is a helper for defining view-like types that offer a container-like interface.

It is parameterized with the type that is derived from it.

🔗

namespace std::ranges { template<class D> requires is_class_v<D> && same_as<D, remove_cv_t<D>> class view_interface { private: constexpr D& derived() noexcept { // exposition only return static_cast<D&>(*this); } constexpr const D& derived() const noexcept { // exposition only return static_cast<const D&>(*this); } public: constexpr bool empty() requires forward_range<D> { return ranges::begin(derived()) == ranges::end(derived()); } constexpr bool empty() const requires forward_range<const D> { return ranges::begin(derived()) == ranges::end(derived()); } constexpr explicit operator bool() requires requires { ranges::empty(derived()); } { return !ranges::empty(derived()); } constexpr explicit operator bool() const requires requires { ranges::empty(derived()); } { return !ranges::empty(derived()); } constexpr auto data() requires contiguous_iterator<iterator_t<D>> { return to_address(ranges::begin(derived())); } constexpr auto data() const requires range<const D> && contiguous_iterator<iterator_t<const D>> { return to_address(ranges::begin(derived())); } constexpr auto size() requires forward_range<D> && sized_sentinel_for<sentinel_t<D>, iterator_t<D>> { return ranges::end(derived()) - ranges::begin(derived()); } constexpr auto size() const requires forward_range<const D> && sized_sentinel_for<sentinel_t<const D>, iterator_t<const D>> { return ranges::end(derived()) - ranges::begin(derived()); } constexpr decltype(auto) front() requires forward_range<D>; constexpr decltype(auto) front() const requires forward_range<const D>; constexpr decltype(auto) back() requires bidirectional_range<D> && common_range<D>; constexpr decltype(auto) back() const requires bidirectional_range<const D> && common_range<const D>; template<random_access_range R = D> constexpr decltype(auto) operator[](range_difference_t<R> n) { return ranges::begin(derived())[n]; } template<random_access_range R = const D> constexpr decltype(auto) operator[](range_difference_t<R> n) const { return ranges::begin(derived())[n]; } }; }

The template parameter D for view_interface may be an incomplete type.

Before any member of the resulting specialization of view_interface other than special member functions is referenced, D shall be complete, and model both derived_from<view_interface<D>> and view .

24.5.3.2 Members [view.interface.members]

🔗

constexpr decltype(auto) front() requires forward_range<D>;
constexpr decltype(auto) front() const requires forward_range<const D>;

Preconditions: !empty() is true.

Effects: Equivalent to: return *ranges::begin(derived());

🔗

constexpr decltype(auto) back() requires bidirectional_range<D> && common_range<D>;
constexpr decltype(auto) back() const
  requires bidirectional_range<const D> && common_range<const D>;

Preconditions: !empty() is true.

Effects: Equivalent to: return *ranges::prev(ranges::end(derived()));

24.5.4 Sub-ranges [range.subrange]

24.5.4.1 General [range.subrange.general]

The subrange class template combines together an iterator and a sentinel into a single object that models the view concept.

Additionally, it models the sized_range concept when the final template parameter is subrange_kind::sized.

🔗

namespace std::ranges { template<class From, class To> concept convertible-to-non-slicing = // exposition only convertible_to<From, To> && !(is_pointer_v<decay_t<From>> && is_pointer_v<decay_t<To>> && different-from<remove_pointer_t<decay_t<From>>, remove_pointer_t<decay_t<To>>>); template<class T> concept pair-like = // exposition only !is_reference_v<T> && requires(T t) { typename tuple_size<T>::type; // ensures tuple_size<T> is complete requires derived_from<tuple_size<T>, integral_constant<size_t, 2>>; typename tuple_element_t<0, remove_const_t<T>>; typename tuple_element_t<1, remove_const_t<T>>; { std::get<0>(t) } -> convertible_to<const tuple_element_t<0, T>&>; { std::get<1>(t) } -> convertible_to<const tuple_element_t<1, T>&>; }; template<class T, class U, class V> concept pair-like-convertible-from = // exposition only !range<T> && pair-like<T> && constructible_from<T, U, V> && convertible-to-non-slicing<U, tuple_element_t<0, T>> && convertible_to<V, tuple_element_t<1, T>>; template<input_or_output_iterator I, sentinel_for S = I, subrange_kind K = sized_sentinel_for<S, I> ? subrange_kind::sized : subrange_kind::unsized> requires (K == subrange_kind::sized || !sized_sentinel_for<S, I>) class subrange : public view_interface<subrange<I, S, K>> { private: static constexpr bool StoreSize = // exposition only K == subrange_kind::sized && !sized_sentinel_for<S, I>; I begin_ = I(); // exposition only S end_ = S(); // exposition only make-unsigned-like-t<iter_difference_t> size_ = 0; // exposition only; present only // when StoreSize is true public: subrange() requires default_initializable = default; constexpr subrange(convertible-to-non-slicing auto i, S s) requires (!StoreSize); constexpr subrange(convertible-to-non-slicing auto i, S s, make-unsigned-like-t<iter_difference_t> n) requires (K == subrange_kind::sized); template<different-from<subrange> R> requires borrowed_range<R> && convertible-to-non-slicing<iterator_t<R>, I> && convertible_to<sentinel_t<R>, S> constexpr subrange(R&& r) requires (!StoreSize || sized_range<R>); template<borrowed_range R> requires convertible-to-non-slicing<iterator_t<R>, I> && convertible_to<sentinel_t<R>, S> constexpr subrange(R&& r, make-unsigned-like-t<iter_difference_t> n) requires (K == subrange_kind::sized) : subrange{ranges::begin(r), ranges::end(r), n} {} template<different-from<subrange> PairLike> requires pair-like-convertible-from<PairLike, const I&, const S&> constexpr operator PairLike() const; constexpr I begin() const requires copyable; [[nodiscard]] constexpr I begin() requires (!copyable); constexpr S end() const; constexpr bool empty() const; constexpr make-unsigned-like-t<iter_difference_t> size() const requires (K == subrange_kind::sized); [[nodiscard]] constexpr subrange next(iter_difference_t n = 1) const & requires forward_iterator; [[nodiscard]] constexpr subrange next(iter_difference_t n = 1) &&; [[nodiscard]] constexpr subrange prev(iter_difference_t n = 1) const requires bidirectional_iterator; constexpr subrange& advance(iter_difference_t n); }; template<input_or_output_iterator I, sentinel_for S> subrange(I, S) -> subrange<I, S>; template<input_or_output_iterator I, sentinel_for S> subrange(I, S, make-unsigned-like-t<iter_difference_t>) -> subrange<I, S, subrange_kind::sized>; template<borrowed_range R> subrange(R&&) -> subrange<iterator_t<R>, sentinel_t<R>, (sized_range<R> || sized_sentinel_for<sentinel_t<R>, iterator_t<R>>) ? subrange_kind::sized : subrange_kind::unsized>; template<borrowed_range R> subrange(R&&, make-unsigned-like-t<range_difference_t<R>>) -> subrange<iterator_t<R>, sentinel_t<R>, subrange_kind::sized>; template<size_t N, class I, class S, subrange_kind K> requires (N < 2) constexpr auto get(const subrange<I, S, K>& r); template<size_t N, class I, class S, subrange_kind K> requires (N < 2) constexpr auto get(subrange<I, S, K>&& r); } namespace std { using ranges::get; }

24.5.4.2 Constructors and conversions [range.subrange.ctor]

🔗

constexpr subrange(convertible-to-non-slicing<I> auto i, S s) requires (!StoreSize);

Preconditions: [i, s) is a valid range.

Effects: Initializes begin_ with std::move(i) and end_ with s.

🔗

constexpr subrange(convertible-to-non-slicing<I> auto i, S s,
                   make-unsigned-like-t<iter_difference_t<I>> n)
  requires (K == subrange_kind::sized);

Preconditions: [i, s) is a valid range, and n == to-unsigned-like(ranges::distance(i, s)) is true.

Effects: Initializes begin_ with std::move(i) and end_ with s.

If StoreSize is true, initializes size_ with n.

[Note 1:

Accepting the length of the range and storing it to later return from size() enables subrange to model sized_range even when it stores an iterator and sentinel that do not model sized_sentinel_for .

— end note]

🔗

template<different-from<subrange> R>
  requires borrowed_range<R> &&
           convertible-to-non-slicing<iterator_t<R>, I> &&
           convertible_to<sentinel_t<R>, S>
constexpr subrange(R&& r) requires (!StoreSize || sized_range<R>);

Effects: Equivalent to:

(6.1)
If StoreSize is true, subrange(r, ranges::size(r)).
(6.2)
Otherwise, subrange(ranges::begin(r), ranges::end(r)).

🔗

template<different-from<subrange> PairLike>
  requires pair-like-convertible-from<PairLike, const I&, const S&>
constexpr operator PairLike() const;

Effects: Equivalent to: return PairLike(begin_, end_);

24.5.4.3 Accessors [range.subrange.access]

🔗

constexpr I begin() const requires copyable<I>;

Effects: Equivalent to: return begin_;

🔗

[[nodiscard]] constexpr I begin() requires (!copyable<I>);

Effects: Equivalent to: return std::move(begin_);

🔗

constexpr S end() const;

Effects: Equivalent to: return end_;

🔗

constexpr bool empty() const;

Effects: Equivalent to: return begin_ == end_;

🔗

constexpr make-unsigned-like-t<iter_difference_t<I>> size() const
  requires (K == subrange_kind::sized);

Effects:

(5.1)
If StoreSize is true, equivalent to: return size_;
(5.2)
Otherwise, equivalent to: return to-unsigned-like(end_ - begin_);

🔗

[[nodiscard]] constexpr subrange next(iter_difference_t<I> n = 1) const &
  requires forward_iterator<I>;

Effects: Equivalent to: auto tmp = *this; tmp.advance(n); return tmp;

🔗

[[nodiscard]] constexpr subrange next(iter_difference_t<I> n = 1) &&;

Effects: Equivalent to: advance(n); return std::move(*this);

🔗

[[nodiscard]] constexpr subrange prev(iter_difference_t<I> n = 1) const
  requires bidirectional_iterator<I>;

Effects: Equivalent to: auto tmp = *this; tmp.advance(-n); return tmp;

🔗

constexpr subrange& advance(iter_difference_t<I> n);

Effects: Equivalent to: if constexpr (bidirectional_iterator) { if (n < 0) { ranges::advance(begin_, n); if constexpr (StoreSize) size_ += to-unsigned-like(-n); return *this; } } auto d = n - ranges::advance(begin_, n, end_); if constexpr (StoreSize) size_ -= to-unsigned-like(d); return *this;

🔗

template<size_t N, class I, class S, subrange_kind K>
  requires (N < 2)
  constexpr auto get(const subrange<I, S, K>& r);
template<size_t N, class I, class S, subrange_kind K>
  requires (N < 2)
  constexpr auto get(subrange<I, S, K>&& r);

Effects: Equivalent to: if constexpr (N == 0) return r.begin(); else return r.end();

24.5.5 Dangling iterator handling [range.dangling]

The tag type dangling is used together with the template aliases borrowed_iterator_t and borrowed_subrange_t.

When an algorithm that typically returns an iterator into, or a subrange of, a range argument is called with an rvalue range argument that does not model borrowed_range ([range.range]), the return value possibly refers to a range whose lifetime has ended.

In such cases, the tag type dangling is returned instead of an iterator or subrange.

🔗

namespace std::ranges { struct dangling { constexpr dangling() noexcept = default; constexpr dangling(auto&&...) noexcept { } }; }

[Example 1: vector<int> f(); auto result1 = ranges::find(f(), 42); // #1 static_assert(same_as<decltype(result1), ranges::dangling>); auto vec = f(); auto result2 = ranges::find(vec, 42); // #2 static_assert(same_as<decltype(result2), vector<int>::iterator>); auto result3 = ranges::find(subrange{vec}, 42); // #3 static_assert(same_as<decltype(result3), vector<int>::iterator>);

The call to ranges::find at #1 returns ranges::dangling since f() is an rvalue vector; it is possible for the vector to be destroyed before a returned iterator is dereferenced.

However, the calls at #2 and #3 both return iterators since the lvalue vec and specializations of subrange model borrowed_range .

— end example]

For a type R that models range:

(3.1)
if R models borrowed_range, then borrowed_iterator_t<R> denotes iterator_t<R>, and borrowed_subrange_t<R> denotes subrange<iterator_t<R>>;
(3.2)
otherwise, both borrowed_iterator_t<R> and borrowed_subrange_t<R> denote dangling.

24.6 Range factories [range.factories]

24.6.1 General [range.factories.general]

Subclause [range.factories] defines range factories, which are utilities to create a view .

Range factories are declared in namespace std::ranges::views.

24.6.2 Empty view [range.empty]

24.6.2.1 Overview [range.empty.overview]

empty_view produces a view of no elements of a particular type.

[Example 1: auto e = views::empty<int>; static_assert(ranges::empty(e)); static_assert(0 == e.size()); — end example]

24.6.2.2 Class template empty_view [range.empty.view]

🔗

namespace std::ranges { template<class T> requires is_object_v<T> class empty_view : public view_interface<empty_view<T>> { public: static constexpr T* begin() noexcept { return nullptr; } static constexpr T* end() noexcept { return nullptr; } static constexpr T* data() noexcept { return nullptr; } static constexpr size_t size() noexcept { return 0; } static constexpr bool empty() noexcept { return true; } }; }

24.6.3 Single view [range.single]

24.6.3.1 Overview [range.single.overview]

single_view produces a view that contains exactly one element of a specified value.

The name views::single denotes a customization point object ([customization.point.object]).

Given a subexpression E, the expression views::single(E) is expression-equivalent to single_view<decay_t<decltype((E))>>(E).

[Example 1: for (int i : views::single(4)) cout << i; // prints 4 — end example]

24.6.3.2 Class template single_view [range.single.view]

🔗

namespace std::ranges { template<copy_constructible T> requires is_object_v<T> class single_view : public view_interface<single_view<T>> { private: copyable-box<T> value_; // exposition only (see [range.copy.wrap]) public: single_view() requires default_initializable<T> = default; constexpr explicit single_view(const T& t); constexpr explicit single_view(T&& t); template<class... Args> requires constructible_from<T, Args...> constexpr explicit single_view(in_place_t, Args&&... args); constexpr T* begin() noexcept; constexpr const T* begin() const noexcept; constexpr T* end() noexcept; constexpr const T* end() const noexcept; static constexpr size_t size() noexcept; constexpr T* data() noexcept; constexpr const T* data() const noexcept; }; template<class T> single_view(T) -> single_view<T>; }

🔗

constexpr explicit single_view(const T& t);

Effects: Initializes value_ with t.

🔗

constexpr explicit single_view(T&& t);

Effects: Initializes value_ with std::move(t).

🔗

template<class... Args>
  requires constructible_from<T, Args...>
constexpr explicit single_view(in_place_t, Args&&... args);

Effects: Initializes value_ as if by value_{in_place, std::forward<Args>(args)...}.

🔗

constexpr T* begin() noexcept;
constexpr const T* begin() const noexcept;

Effects: Equivalent to: return data();

🔗

constexpr T* end() noexcept;
constexpr const T* end() const noexcept;

Effects: Equivalent to: return data() + 1;

🔗

static constexpr size_t size() noexcept;

Effects: Equivalent to: return 1;

🔗

constexpr T* data() noexcept;
constexpr const T* data() const noexcept;

Effects: Equivalent to: return value_.operator->();

24.6.4 Iota view [range.iota]

24.6.4.1 Overview [range.iota.overview]

iota_view generates a sequence of elements by repeatedly incrementing an initial value.

The name views::iota denotes a customization point object ([customization.point.object]).

Given subexpressions E and F, the expressions views::iota(E) and views::iota(E, F) are expression-equivalent to iota_view(E) and iota_view(E, F), respectively.

[Example 1: for (int i : views::iota(1, 10)) cout << i << ' '; // prints: 1 2 3 4 5 6 7 8 9 — end example]

24.6.4.2 Class template iota_view [range.iota.view]

🔗

namespace std::ranges { template<class I> concept decrementable = see below; // exposition only template<class I> concept advanceable = see below; // exposition only template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t> requires weakly-equality-comparable-with<W, Bound> && copyable<W> class iota_view : public view_interface<iota_view<W, Bound>> { private: // [range.iota.iterator], class iota_view::iterator struct iterator; // exposition only // [range.iota.sentinel], class iota_view::sentinel struct sentinel; // exposition only W value_ = W(); // exposition only Bound bound_ = Bound(); // exposition only public: iota_view() requires default_initializable<W> = default; constexpr explicit iota_view(W value); constexpr iota_view(type_identity_t<W> value, type_identity_t<Bound> bound); constexpr iota_view(iterator first, see below last); constexpr iterator begin() const; constexpr auto end() const; constexpr iterator end() const requires same_as<W, Bound>; constexpr auto size() const requires see below; }; template<class W, class Bound> requires (!is-integer-like<W> || !is-integer-like<Bound> || (is-signed-integer-like<W> == is-signed-integer-like<Bound>)) iota_view(W, Bound) -> iota_view<W, Bound>; }

Let IOTA-DIFF-T(W) be defined as follows:

(1.1)
If W is not an integral type, or if it is an integral type and sizeof(iter_difference_t<W>) is greater than sizeof(W), then IOTA-DIFF-T(W) denotes iter_difference_t<W>.
(1.2)
Otherwise, IOTA-DIFF-T(W) is a signed integer type of width greater than the width of W if such a type exists.
(1.3)
Otherwise, IOTA-DIFF-T(W) is an unspecified signed-integer-like type ([iterator.concept.winc]) of width not less than the width of W.

[Note 1:
It is unspecified whether this type satisfies weakly_incrementable .
— end note]

The exposition-only decrementable concept is equivalent to:

🔗

template<class I>
  concept decrementable =               // exposition only
    incrementable<I> && requires(I i) {
      { --i } -> same_as<I&>;
      { i-- } -> same_as<I>;
    };

When an object is in the domain of both pre- and post-decrement, the object is said to be decrementable.

Let a and b be equal objects of type I.

I models decrementable only if

(4.1)
If a and b are decrementable, then the following are all true:
- (4.1.1)
  addressof(--a) == addressof(a)
- (4.1.2)
  bool(a-- == b)
- (4.1.3)
  bool(((void)a--, a) == --b)
- (4.1.4)
  bool(++(--a) == b).
(4.2)
If a and b are incrementable, then bool(--(++a) == b).

The exposition-only advanceable concept is equivalent to:

🔗

template<class I>
  concept advanceable =                 // exposition only
    decrementable<I> && totally_ordered<I> &&
    requires(I i, const I j, const IOTA-DIFF-T(I) n) {
      { i += n } -> same_as<I&>;
      { i -= n } -> same_as<I&>;
      I(j + n);
      I(n + j);
      I(j - n);
      { j - j } -> convertible_to<IOTA-DIFF-T(I)>;
    };

Let D be IOTA-DIFF-T(I).

Let a and b be objects of type I such that b is reachable from a after n applications of ++a, for some value n of type D.

I models advanceable only if

(a += n) is equal to b.
addressof(a += n) is equal to addressof(a).
I(a + n) is equal to (a += n).
For any two positive values x and y of type D, if I(a + D(x + y)) is well-defined, then I(a + D(x + y)) is equal to I(I(a + x) + y).
I(a + D(0)) is equal to a.
If I(a + D(n - 1)) is well-defined, then I(a + n) is equal to [](I c) { return ++c; }(I(a + D(n - 1))).
(b += -n) is equal to a.
(b -= n) is equal to a.
addressof(b -= n) is equal to addressof(b).
I(b - n) is equal to (b -= n).
D(b - a) is equal to n.
D(a - b) is equal to D(-n).
bool(a <= b) is true.

🔗

constexpr explicit iota_view(W value);

Preconditions: Bound denotes unreachable_sentinel_t or Bound() is reachable from value.

Effects: Initializes value_ with value.

🔗

constexpr iota_view(type_identity_t<W> value, type_identity_t<Bound> bound);

Preconditions: Bound denotes unreachable_sentinel_t or bound is reachable from value.

When W and Bound model totally_ordered_with, then bool(value <= bound) is true.

Effects: Initializes value_ with value and bound_ with bound.

🔗

constexpr iota_view(iterator first, see below last);

Effects: Equivalent to:

(10.1)
If same_as<W, Bound> is true, iota_view(first.value_, last.value_).
(10.2)
Otherwise, if Bound denotes unreachable_sentinel_t, iota_view(first.value_, last).
(10.3)
Otherwise, iota_view(first.value_, last.bound_).

Remarks: The type of last is:

(11.1)
If same_as<W, Bound> is true, iterator.
(11.2)
Otherwise, if Bound denotes unreachable_sentinel_t, Bound.
(11.3)
Otherwise, sentinel.

🔗

constexpr iterator begin() const;

Effects: Equivalent to: return iterator{value_};

🔗

constexpr auto end() const;

Effects: Equivalent to: if constexpr (same_as<Bound, unreachable_sentinel_t>) return unreachable_sentinel; else return sentinel{bound_};

🔗

constexpr iterator end() const requires same_as<W, Bound>;

Effects: Equivalent to: return iterator{bound_};

🔗

constexpr auto size() const requires see below;

Effects: Equivalent to: if constexpr (is-integer-like<W> && is-integer-like<Bound>) return (value_ < 0) ? ((bound_ < 0) ? to-unsigned-like(-value_) - to-unsigned-like(-bound_) : to-unsigned-like(bound_) + to-unsigned-like(-value_)) : to-unsigned-like(bound_) - to-unsigned-like(value_); else return to-unsigned-like(bound_ - value_);

Remarks: The expression in the requires-clause is equivalent to: (same_as<W, Bound> && advanceable<W>) || (integral<W> && integral<Bound>) || sized_sentinel_for<Bound, W>

24.6.4.3 Class iota_view::iterator [range.iota.iterator]

🔗

namespace std::ranges { template<weakly_incrementable W, semiregular Bound> requires weakly-equality-comparable-with<W, Bound> && copyable<W> struct iota_view<W, Bound>::iterator { private: W value_ = W(); // exposition only public: using iterator_concept = see below; using iterator_category = input_iterator_tag; // present only if W models incrementable using value_type = W; using difference_type = IOTA-DIFF-T(W); iterator() requires default_initializable<W> = default; constexpr explicit iterator(W value); constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>); constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires incrementable<W>; constexpr iterator& operator--() requires decrementable<W>; constexpr iterator operator--(int) requires decrementable<W>; constexpr iterator& operator+=(difference_type n) requires advanceable<W>; constexpr iterator& operator-=(difference_type n) requires advanceable<W>; constexpr W operator[](difference_type n) const requires advanceable<W>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<W>; friend constexpr bool operator<(const iterator& x, const iterator& y) requires totally_ordered<W>; friend constexpr bool operator>(const iterator& x, const iterator& y) requires totally_ordered<W>; friend constexpr bool operator<=(const iterator& x, const iterator& y) requires totally_ordered<W>; friend constexpr bool operator>=(const iterator& x, const iterator& y) requires totally_ordered<W>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires totally_ordered<W> && three_way_comparable<W>; friend constexpr iterator operator+(iterator i, difference_type n) requires advanceable<W>; friend constexpr iterator operator+(difference_type n, iterator i) requires advanceable<W>; friend constexpr iterator operator-(iterator i, difference_type n) requires advanceable<W>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires advanceable<W>; }; }

iterator::iterator_concept is defined as follows:

(1.1)
If W models advanceable, then iterator_concept is random_access_iterator_tag.
(1.2)
Otherwise, if W models decrementable, then iterator_concept is bidirectional_iterator_tag.
(1.3)
Otherwise, if W models incrementable, then iterator_concept is forward_iterator_tag.
(1.4)
Otherwise, iterator_concept is input_iterator_tag.

[Note 1:

Overloads for iter_move and iter_swap are omitted intentionally.

— end note]

🔗

constexpr explicit iterator(W value);

Effects: Initializes value_ with value.

🔗

constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);

Effects: Equivalent to: return value_;

[Note 2:

The noexcept clause is needed by the default iter_move implementation.

— end note]

🔗

constexpr iterator& operator++();

Effects: Equivalent to: ++value_; return *this;

🔗

constexpr void operator++(int);

Effects: Equivalent to ++*this.

🔗

constexpr iterator operator++(int) requires incrementable<W>;

Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;

🔗

constexpr iterator& operator--() requires decrementable<W>;

Effects: Equivalent to: --value_; return *this;

🔗

constexpr iterator operator--(int) requires decrementable<W>;

Effects: Equivalent to: auto tmp = *this; --*this; return tmp;

🔗

constexpr iterator& operator+=(difference_type n)
  requires advanceable<W>;

Effects: Equivalent to: if constexpr (is-integer-like<W> && !is-signed-integer-like<W>) { if (n >= difference_type(0)) value_ += static_cast<W>(n); else value_ -= static_cast<W>(-n); } else { value_ += n; } return *this;

🔗

constexpr iterator& operator-=(difference_type n)
  requires advanceable<W>;

Effects: Equivalent to: if constexpr (is-integer-like<W> && !is-signed-integer-like<W>) { if (n >= difference_type(0)) value_ -= static_cast<W>(n); else value_ += static_cast<W>(-n); } else { value_ -= n; } return *this;

🔗

constexpr W operator[](difference_type n) const
  requires advanceable<W>;

Effects: Equivalent to: return W(value_ + n);

🔗

friend constexpr bool operator==(const iterator& x, const iterator& y)
  requires equality_comparable<W>;

Effects: Equivalent to: return x.value_ == y.value_;

🔗

friend constexpr bool operator<(const iterator& x, const iterator& y)
  requires totally_ordered<W>;

Effects: Equivalent to: return x.value_ < y.value_;

🔗

friend constexpr bool operator>(const iterator& x, const iterator& y)
  requires totally_ordered<W>;

Effects: Equivalent to: return y < x;

🔗

friend constexpr bool operator<=(const iterator& x, const iterator& y)
  requires totally_ordered<W>;

Effects: Equivalent to: return !(y < x);

🔗

friend constexpr bool operator>=(const iterator& x, const iterator& y)
  requires totally_ordered<W>;

Effects: Equivalent to: return !(x < y);

🔗

friend constexpr auto operator<=>(const iterator& x, const iterator& y)
  requires totally_ordered<W> && three_way_comparable<W>;

Effects: Equivalent to: return x.value_ <=> y.value_;

🔗

friend constexpr iterator operator+(iterator i, difference_type n)
  requires advanceable<W>;

Effects: Equivalent to: return i += n;

🔗

friend constexpr iterator operator+(difference_type n, iterator i)
  requires advanceable<W>;

Effects: Equivalent to: return i + n;

🔗

friend constexpr iterator operator-(iterator i, difference_type n)
  requires advanceable<W>;

Effects: Equivalent to: return i -= n;

🔗

friend constexpr difference_type operator-(const iterator& x, const iterator& y)
  requires advanceable<W>;

Effects: Equivalent to: using D = difference_type; if constexpr (is-integer-like<W>) { if constexpr (is-signed-integer-like<W>) return D(D(x.value_) - D(y.value_)); else return (y.value_ > x.value_) ? D(-D(y.value_ - x.value_)) : D(x.value_ - y.value_); } else { return x.value_ - y.value_; }

24.6.4.4 Class iota_view::sentinel [range.iota.sentinel]

🔗

namespace std::ranges { template<weakly_incrementable W, semiregular Bound> requires weakly-equality-comparable-with<W, Bound> && copyable<W> struct iota_view<W, Bound>::sentinel { private: Bound bound_ = Bound(); // exposition only public: sentinel() = default; constexpr explicit sentinel(Bound bound); friend constexpr bool operator==(const iterator& x, const sentinel& y); friend constexpr iter_difference_t<W> operator-(const iterator& x, const sentinel& y) requires sized_sentinel_for<Bound, W>; friend constexpr iter_difference_t<W> operator-(const sentinel& x, const iterator& y) requires sized_sentinel_for<Bound, W>; }; }

🔗

constexpr explicit sentinel(Bound bound);

Effects: Initializes bound_ with bound.

🔗

friend constexpr bool operator==(const iterator& x, const sentinel& y);

Effects: Equivalent to: return x.value_ == y.bound_;

🔗

friend constexpr iter_difference_t<W> operator-(const iterator& x, const sentinel& y)
  requires sized_sentinel_for<Bound, W>;

Effects: Equivalent to: return x.value_ - y.bound_;

🔗

friend constexpr iter_difference_t<W> operator-(const sentinel& x, const iterator& y)
  requires sized_sentinel_for<Bound, W>;

Effects: Equivalent to: return -(y - x);

24.6.5 Istream view [range.istream]

24.6.5.1 Overview [range.istream.overview]

basic_istream_view models input_range and reads (using operator>>) successive elements from its corresponding input stream.

[Example 1: auto ints = istringstream{"0 1 2 3 4"}; ranges::copy(ranges::istream_view<int>(ints), ostream_iterator<int>{cout, "-"}); // prints 0-1-2-3-4- — end example]

24.6.5.2 Class template basic_istream_view [range.istream.view]

🔗

namespace std::ranges { template<class Val, class CharT, class Traits> concept stream-extractable = // exposition only requires(basic_istream<CharT, Traits>& is, Val& t) { is >> t; }; template<movable Val, class CharT, class Traits> requires default_initializable<Val> && stream-extractable<Val, CharT, Traits> class basic_istream_view : public view_interface<basic_istream_view<Val, CharT, Traits>> { public: constexpr explicit basic_istream_view(basic_istream<CharT, Traits>& stream); constexpr auto begin() { *stream_ >> value_; return iterator{*this}; } constexpr default_sentinel_t end() const noexcept; private: struct iterator; // exposition only basic_istream<CharT, Traits>* stream_; // exposition only Val value_; // exposition only }; }

🔗

constexpr explicit basic_istream_view(basic_istream<CharT, Traits>& stream);

Effects: Initializes stream_ with addressof(stream).

🔗

constexpr default_sentinel_t end() const noexcept;

Effects: Equivalent to: return default_sentinel;

🔗

template<class Val, class CharT, class Traits>
basic_istream_view<Val, CharT, Traits> istream_view(basic_istream<CharT, Traits>& s);

Effects: Equivalent to: return basic_istream_view<Val, CharT, Traits>{s};

24.6.5.3 Class template basic_istream_view::iterator [range.istream.iterator]

🔗

namespace std::ranges { template<movable Val, class CharT, class Traits> requires default_initializable<Val> && stream-extractable<Val, CharT, Traits> class basic_istream_view<Val, CharT, Traits>::iterator { // exposition only public: using iterator_concept = input_iterator_tag; using difference_type = ptrdiff_t; using value_type = Val; constexpr explicit iterator(basic_istream_view& parent) noexcept; iterator(const iterator&) = delete; iterator(iterator&&) = default; iterator& operator=(const iterator&) = delete; iterator& operator=(iterator&&) = default; iterator& operator++(); void operator++(int); Val& operator*() const; friend bool operator==(const iterator& x, default_sentinel_t); private: basic_istream_view* parent_; // exposition only }; }

🔗

constexpr explicit iterator(basic_istream_view& parent) noexcept;

Effects: Initializes parent_ with addressof(parent).

🔗

iterator& operator++();

Effects: Equivalent to: *parent_->stream_ >> parent_->value_; return *this;

🔗

void operator++(int);

Effects: Equivalent to ++*this.

🔗

Val& operator*() const;

Effects: Equivalent to: return parent_->value_;

🔗

friend bool operator==(const iterator& x, default_sentinel_t);

Effects: Equivalent to: return !*x.parent_->stream_;

24.7 Range adaptors [range.adaptors]

24.7.1 General [range.adaptors.general]

Subclause [range.adaptors] defines range adaptors, which are utilities that transform a range into a view with custom behaviors.

These adaptors can be chained to create pipelines of range transformations that evaluate lazily as the resulting view is iterated.

Range adaptors are declared in namespace std::ranges::views.

The bitwise OR operator is overloaded for the purpose of creating adaptor chain pipelines.

The adaptors also support function call syntax with equivalent semantics.

[Example 1: vector<int> ints{0,1,2,3,4,5}; auto even = [](int i) { return 0 == i % 2; }; auto square = [](int i) { return i * i; }; for (int i : ints | views::filter(even) | views::transform(square)) { cout << i << ' '; // prints: 0 4 16 } assert(ranges::equal(ints | views::filter(even), views::filter(ints, even))); — end example]

24.7.2 Range adaptor objects [range.adaptor.object]

A range adaptor closure object is a unary function object that accepts a viewable_range argument and returns a view .

For a range adaptor closure object C and an expression R such that decltype((R)) models viewable_range, the following expressions are equivalent and yield a view: C(R) R | C

Given an additional range adaptor closure object D, the expression C | D produces another range adaptor closure object E.

E is a perfect forwarding call wrapper ([func.require]) with the following properties:

(1.1)
Its target object is an object d of type decay_t<decltype((D))> direct-non-list-initialized with D.
(1.2)
It has one bound argument entity, an object c of type decay_t<decltype((C))> direct-non-list-initialized with C.
(1.3)
Its call pattern is d(c(arg)), where arg is the argument used in a function call expression of E.

The expression C | D is well-formed if and only if the initializations of the state entities of E are all well-formed.

A range adaptor object is a customization point object ([customization.point.object]) that accepts a viewable_range as its first argument and returns a view .

If a range adaptor object accepts only one argument, then it is a range adaptor closure object.

If a range adaptor object adaptor accepts more than one argument, then let range be an expression such that decltype((range)) models viewable_range, let args... be arguments such that adaptor(range, args...) is a well-formed expression as specified in the rest of subclause [range.adaptors], and let BoundArgs be a pack that denotes decay_t<decltype((args))>....

The expression adaptor(args...) produces a range adaptor closure object f that is a perfect forwarding call wrapper with the following properties:

(4.1)
Its target object is a copy of adaptor.
(4.2)
Its bound argument entities bound_args consist of objects of types BoundArgs... direct-non-list-initialized with std::forward<decltype((args))>(args)..., respectively.
(4.3)
Its call pattern is adaptor(r, bound_args...), where r is the argument used in a function call expression of f.

The expression adaptor(args...) is well-formed if and only if the initialization of the bound argument entities of the result, as specified above, are all well-formed.

24.7.3 Copyable wrapper [range.copy.wrap]

Many types in this subclause are specified in terms of an exposition-only class template copyable-box.

copyable-box<T> behaves exactly like optional<T> with the following differences:

(1.1)
copyable-box<T> constrains its type parameter T with copy_constructible<T> && is_object_v<T>.
(1.2)
The default constructor of copyable-box<T> is equivalent to: constexpr copyable-box() noexcept(is_nothrow_default_constructible_v<T>) requires default_initializable<T> : copyable-box{in_place} { }
(1.3)
If copyable<T> is not modeled, the copy assignment operator is equivalent to: copyable-box& operator=(const copyable-box& that) noexcept(is_nothrow_copy_constructible_v<T>) { if (this != addressof(that)) { if (that) emplace(*that); else reset(); } return *this; }
(1.4)
If movable<T> is not modeled, the move assignment operator is equivalent to: copyable-box& operator=(copyable-box&& that) noexcept(is_nothrow_move_constructible_v<T>) { if (this != addressof(that)) { if (that) emplace(std::move(*that)); else reset(); } return *this; }

Recommended practice: copyable-box<T> should store only a T if either T models copyable or is_nothrow_move_constructible_v<T> && is_nothrow_copy_constructible_v<T> is true.

24.7.4 Non-propagating cache [range.nonprop.cache]

Some types in subclause [range.adaptors] are specified in terms of an exposition-only class template non-propagating-cache.

non-propagating-cache<T> behaves exactly like optional<T> with the following differences:

(1.1)
non-propagating-cache<T> constrains its type parameter T with is_object_v<T>.
(1.2)
The copy constructor is equivalent to: constexpr non-propagating-cache(const non-propagating-cache&) noexcept { }
(1.3)
The move constructor is equivalent to: constexpr non-propagating-cache(non-propagating-cache&& other) noexcept { other.reset(); }
(1.4)
The copy assignment operator is equivalent to: constexpr non-propagating-cache& operator=(const non-propagating-cache& other) noexcept { if (addressof(other) != this) reset(); return *this; }
(1.5)
The move assignment operator is equivalent to: constexpr non-propagating-cache& operator=(non-propagating-cache&& other) noexcept { reset(); other.reset(); return *this; }
(1.6)
non-propagating-cache<T> has an additional member function template specified as follows:
🔗
template<class I> constexpr T& emplace-deref(const I& i); // exposition only
Mandates: The declaration T t(*i); is well-formed for some invented variable t.

[Note 1:
If *i is a prvalue of type cv T, there is no requirement that it is movable ([dcl.init.general]).
— end note]
Effects: Calls reset().

Then initializes the contained value as if direct-non-list-initializing an object of type T with the argument *i.
Postconditions: *this contains a value.
Returns: A reference to the new contained value.
Throws: Any exception thrown by the initialization of the contained value.
Remarks: If an exception is thrown during the initialization of T, *this does not contain a value, and the previous value (if any) has been destroyed.

[Note 2:

non-propagating-cache enables an input view to temporarily cache values as it is iterated over.

— end note]

24.7.5 All view [range.all]

24.7.5.1 General [range.all.general]

views::all returns a view that includes all elements of its range argument.

The name views::all denotes a range adaptor object ([range.adaptor.object]).

Given a subexpression E, the expression views::all(E) is expression-equivalent to:

(2.1)
decay-copy(E) if the decayed type of E models view .
(2.2)
Otherwise, ref_view{E} if that expression is well-formed.
(2.3)
Otherwise, subrange{E}.

24.7.5.2 Class template ref_view [range.ref.view]

ref_view is a view of the elements of some other range .

🔗

namespace std::ranges { template<range R> requires is_object_v<R> class ref_view : public view_interface<ref_view<R>> { private: R* r_; // exposition only public: template<different-from<ref_view> T> requires see below constexpr ref_view(T&& t); constexpr R& base() const { return *r_; } constexpr iterator_t<R> begin() const { return ranges::begin(*r_); } constexpr sentinel_t<R> end() const { return ranges::end(*r_); } constexpr bool empty() const requires requires { ranges::empty(*r_); } { return ranges::empty(*r_); } constexpr auto size() const requires sized_range<R> { return ranges::size(*r_); } constexpr auto data() const requires contiguous_range<R> { return ranges::data(*r_); } }; template<class R> ref_view(R&) -> ref_view<R>; }

🔗

template<different-from<ref_view> T>
  requires see below
constexpr ref_view(T&& t);

Effects: Initializes r_ with addressof(static_cast<R&>(std::forward<T>(t))).

Remarks: Let FUN denote the exposition-only functions void FUN(R&); void FUN(R&&) = delete;

The expression in the requires-clause is equivalent to: convertible_to<T, R&> && requires { FUN(declval<T>()); }

24.7.6 Filter view [range.filter]

24.7.6.1 Overview [range.filter.overview]

filter_view presents a view of the elements of an underlying sequence that satisfy a predicate.

The name views::filter denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and P, the expression views::filter(E, P) is expression-equivalent to filter_view(E, P).

[Example 1: vector<int> is{ 0, 1, 2, 3, 4, 5, 6 }; auto evens = views::filter(is, [](int i) { return 0 == i % 2; }); for (int i : evens) cout << i << ' '; // prints: 0 2 4 6 — end example]

24.7.6.2 Class template filter_view [range.filter.view]

🔗

namespace std::ranges { template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class filter_view : public view_interface<filter_view<V, Pred>> { private: V base_ = V(); // exposition only copyable-box<Pred> pred_; // exposition only // [range.filter.iterator], class filter_view::iterator class iterator; // exposition only // [range.filter.sentinel], class filter_view::sentinel class sentinel; // exposition only public: filter_view() requires default_initializable<V> && default_initializable<Pred> = default; constexpr filter_view(V base, Pred pred); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr const Pred& pred() const; constexpr iterator begin(); constexpr auto end() { if constexpr (common_range<V>) return iterator{*this, ranges::end(base_)}; else return sentinel{*this}; } }; template<class R, class Pred> filter_view(R&&, Pred) -> filter_view<views::all_t<R>, Pred>; }

🔗

constexpr filter_view(V base, Pred pred);

Effects: Initializes base_ with std::move(base) and initializes pred_ with std::move(pred).

🔗

constexpr const Pred& pred() const;

Effects: Equivalent to: return *pred_;

🔗

constexpr iterator begin();

Preconditions: pred_.has_value() is true.

Returns: {*this, ranges::find_if(base_, ref(*pred_))}.

Remarks: In order to provide the amortized constant time complexity required by the range concept when filter_view models forward_range, this function caches the result within the filter_view for use on subsequent calls.

24.7.6.3 Class filter_view::iterator [range.filter.iterator]

🔗

namespace std::ranges { template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class filter_view<V, Pred>::iterator { private: iterator_t<V> current_ = iterator_t<V>(); // exposition only filter_view* parent_ = nullptr; // exposition only public: using iterator_concept = see below; using iterator_category = see below; // not always present using value_type = range_value_t<V>; using difference_type = range_difference_t<V>; iterator() requires default_initializable<iterator_t<V>> = default; constexpr iterator(filter_view& parent, iterator_t<V> current); constexpr const iterator_t<V>& base() const &; constexpr iterator_t<V> base() &&; constexpr range_reference_t<V> operator*() const; constexpr iterator_t<V> operator->() const requires has-arrow<iterator_t<V>> && copyable<iterator_t<V>>; constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires forward_range<V>; constexpr iterator& operator--() requires bidirectional_range<V>; constexpr iterator operator--(int) requires bidirectional_range<V>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<iterator_t<V>>; friend constexpr range_rvalue_reference_t<V> iter_move(const iterator& i) noexcept(noexcept(ranges::iter_move(i.current_))); friend constexpr void iter_swap(const iterator& x, const iterator& y) noexcept(noexcept(ranges::iter_swap(x.current_, y.current_))) requires indirectly_swappable<iterator_t<V>>; }; }

Modification of the element a filter_view::iterator denotes is permitted, but results in undefined behavior if the resulting value does not satisfy the filter predicate.

iterator::iterator_concept is defined as follows:

(2.1)
If V models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
(2.2)
Otherwise, if V models forward_range, then iterator_concept denotes forward_iterator_tag.
(2.3)
Otherwise, iterator_concept denotes input_iterator_tag.

The member typedef-name iterator_category is defined if and only if V models forward_range .

In that case, iterator::iterator_category is defined as follows:

(3.1)
Let C denote the type iterator_traits<iterator_t<V>>::iterator_category.
(3.2)
If C models derived_from<bidirectional_iterator_tag>, then iterator_category denotes bidirectional_iterator_tag.
(3.3)
Otherwise, if C models derived_from<forward_iterator_tag>, then iterator_category denotes forward_iterator_tag.
(3.4)
Otherwise, iterator_category denotes C.

🔗

constexpr iterator(filter_view& parent, iterator_t<V> current);

Effects: Initializes current_ with std::move(current) and parent_ with addressof(parent).

🔗

constexpr const iterator_t<V>& base() const &;

Effects: Equivalent to: return current_;

🔗

constexpr iterator_t<V> base() &&;

Effects: Equivalent to: return std::move(current_);

🔗

constexpr range_reference_t<V> operator*() const;

Effects: Equivalent to: return *current_;

🔗

constexpr iterator_t<V> operator->() const
  requires has-arrow<iterator_t<V>> && copyable<iterator_t<V>>;

Effects: Equivalent to: return current_;

🔗

constexpr iterator& operator++();

Effects: Equivalent to: current_ = ranges::find_if(std::move(++current_), ranges::end(parent_->base_), ref(*parent_->pred_)); return *this;

🔗

constexpr void operator++(int);

Effects: Equivalent to ++*this.

🔗

constexpr iterator operator++(int) requires forward_range<V>;

Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;

🔗

constexpr iterator& operator--() requires bidirectional_range<V>;

Effects: Equivalent to: do --current_; while (!invoke(*parent_->pred_, *current_)); return *this;

🔗

constexpr iterator operator--(int) requires bidirectional_range<V>;

Effects: Equivalent to: auto tmp = *this; --*this; return tmp;

🔗

friend constexpr bool operator==(const iterator& x, const iterator& y)
  requires equality_comparable<iterator_t<V>>;

Effects: Equivalent to: return x.current_ == y.current_;

🔗

friend constexpr range_rvalue_reference_t<V> iter_move(const iterator& i)
  noexcept(noexcept(ranges::iter_move(i.current_)));

Effects: Equivalent to: return ranges::iter_move(i.current_);

🔗

friend constexpr void iter_swap(const iterator& x, const iterator& y)
  noexcept(noexcept(ranges::iter_swap(x.current_, y.current_)))
  requires indirectly_swappable<iterator_t<V>>;

Effects: Equivalent to ranges::iter_swap(x.current_, y.current_).

24.7.6.4 Class filter_view::sentinel [range.filter.sentinel]

🔗

namespace std::ranges { template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred> requires view<V> && is_object_v<Pred> class filter_view<V, Pred>::sentinel { private: sentinel_t<V> end_ = sentinel_t<V>(); // exposition only public: sentinel() = default; constexpr explicit sentinel(filter_view& parent); constexpr sentinel_t<V> base() const; friend constexpr bool operator==(const iterator& x, const sentinel& y); }; }

🔗

constexpr explicit sentinel(filter_view& parent);

Effects: Initializes end_ with ranges::end(parent.base_).

🔗

constexpr sentinel_t<V> base() const;

Effects: Equivalent to: return end_;

🔗

friend constexpr bool operator==(const iterator& x, const sentinel& y);

Effects: Equivalent to: return x.current_ == y.end_;

24.7.7 Transform view [range.transform]

24.7.7.1 Overview [range.transform.overview]

transform_view presents a view of an underlying sequence after applying a transformation function to each element.

The name views::transform denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F, the expression views::transform(E, F) is expression-equivalent to transform_view(E, F).

[Example 1: vector<int> is{ 0, 1, 2, 3, 4 }; auto squares = views::transform(is, [](int i) { return i * i; }); for (int i : squares) cout << i << ' '; // prints: 0 1 4 9 16 — end example]

24.7.7.2 Class template transform_view [range.transform.view]

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namespace std::ranges { template<input_range V, copy_constructible F> requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> && can-reference<invoke_result_t<F&, range_reference_t<V>>> class transform_view : public view_interface<transform_view<V, F>> { private: // [range.transform.iterator], class template transform_view::iterator template<bool> struct iterator; // exposition only // [range.transform.sentinel], class template transform_view::sentinel template<bool> struct sentinel; // exposition only V base_ = V(); // exposition only copyable-box<F> fun_; // exposition only public: transform_view() requires default_initializable<V> && default_initializable<F> = default; constexpr transform_view(V base, F fun); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr iterator<false> begin(); constexpr iterator<true> begin() const requires range<const V> && regular_invocable<const F&, range_reference_t<const V>>; constexpr sentinel<false> end(); constexpr iterator<false> end() requires common_range<V>; constexpr sentinel<true> end() const requires range<const V> && regular_invocable<const F&, range_reference_t<const V>>; constexpr iterator<true> end() const requires common_range<const V> && regular_invocable<const F&, range_reference_t<const V>>; constexpr auto size() requires sized_range<V> { return ranges::size(base_); } constexpr auto size() const requires sized_range<const V> { return ranges::size(base_); } }; template<class R, class F> transform_view(R&&, F) -> transform_view<views::all_t<R>, F>; }

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constexpr transform_view(V base, F fun);

Effects: Initializes base_ with std::move(base) and fun_ with std::move(fun).

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constexpr iterator<false> begin();

Effects: Equivalent to: return iterator<false>{*this, ranges::begin(base_)};

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constexpr iterator<true> begin() const
  requires range<const V> &&
           regular_invocable<const F&, range_reference_t<const V>>;

Effects: Equivalent to: return iterator<true>{*this, ranges::begin(base_)};

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constexpr sentinel<false> end();

Effects: Equivalent to: return sentinel<false>{ranges::end(base_)};

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constexpr iterator<false> end() requires common_range<V>;

Effects: Equivalent to: return iterator<false>{*this, ranges::end(base_)};

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constexpr sentinel<true> end() const
  requires range<const V> &&
           regular_invocable<const F&, range_reference_t<const V>>;

Effects: Equivalent to: return sentinel<true>{ranges::end(base_)};

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constexpr iterator<true> end() const
  requires common_range<const V> &&
           regular_invocable<const F&, range_reference_t<const V>>;

Effects: Equivalent to: return iterator<true>{*this, ranges::end(base_)};

24.7.7.3 Class template transform_view::iterator [range.transform.iterator]

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namespace std::ranges { template<input_range V, copy_constructible F> requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> && can-reference<invoke_result_t<F&, range_reference_t<V>>> template<bool Const> class transform_view<V, F>::iterator { private: using Parent = maybe-const<Const, transform_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only iterator_t<Base> current_ = iterator_t<Base>(); // exposition only Parent* parent_ = nullptr; // exposition only public: using iterator_concept = see below; using iterator_category = see below; // not always present using value_type = remove_cvref_t<invoke_result_t<F&, range_reference_t<Base>>>; using difference_type = range_difference_t<Base>; iterator() requires default_initializable<iterator_t<Base>> = default; constexpr iterator(Parent& parent, iterator_t<Base> current); constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>; constexpr const iterator_t<Base>& base() const &; constexpr iterator_t<Base> base() &&; constexpr decltype(auto) operator*() const { return invoke(*parent_->fun_, *current_); } constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires forward_range<Base>; constexpr iterator& operator--() requires bidirectional_range<Base>; constexpr iterator operator--(int) requires bidirectional_range<Base>; constexpr iterator& operator+=(difference_type n) requires random_access_range<Base>; constexpr iterator& operator-=(difference_type n) requires random_access_range<Base>; constexpr decltype(auto) operator[](difference_type n) const requires random_access_range<Base> { return invoke(*parent_->fun_, current_[n]); } friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<iterator_t<Base>>; friend constexpr bool operator<(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator>(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator<=(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr bool operator>=(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires random_access_range<Base> && three_way_comparable<iterator_t<Base>>; friend constexpr iterator operator+(iterator i, difference_type n) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, iterator i) requires random_access_range<Base>; friend constexpr iterator operator-(iterator i, difference_type n) requires random_access_range<Base>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires sized_sentinel_for<iterator_t<Base>, iterator_t<Base>>; friend constexpr decltype(auto) iter_move(const iterator& i) noexcept(noexcept(invoke(*i.parent_->fun_, *i.current_))) { if constexpr (is_lvalue_reference_v<decltype(*i)>) return std::move(*i); else return *i; } }; }

iterator::iterator_concept is defined as follows:

(1.1)
If Base models random_access_range, then iterator_concept denotes random_access_iterator_tag.
(1.2)
Otherwise, if Base models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
(1.3)
Otherwise, if Base models forward_range, then iterator_concept denotes forward_iterator_tag.
(1.4)
Otherwise, iterator_concept denotes input_iterator_tag.

The member typedef-name iterator_category is defined if and only if Base models forward_range .

In that case, iterator::iterator_category is defined as follows: Let C denote the type iterator_traits<iterator_t<Base>>::iterator_category.

(2.1)
If is_lvalue_reference_v<invoke_result_t<F&, range_reference_t<Base>>> is true, then
- (2.1.1)
 if C models derived_from<contiguous_iterator_tag>, iterator_category denotes random_access_iterator_tag;
- (2.1.2)
 otherwise, iterator_category denotes C.
(2.2)
Otherwise, iterator_category denotes input_iterator_tag.

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constexpr iterator(Parent& parent, iterator_t<Base> current);

Effects: Initializes current_ with std::move(current) and parent_ with addressof(parent).

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constexpr iterator(iterator<!Const> i)
  requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>;

Effects: Initializes current_ with std::move(i.current_) and parent_ with i.parent_.

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constexpr const iterator_t<Base>& base() const &;

Effects: Equivalent to: return current_;

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constexpr iterator_t<Base> base() &&;

Effects: Equivalent to: return std::move(current_);

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constexpr iterator& operator++();

Effects: Equivalent to: ++current_; return *this;

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constexpr void operator++(int);

Effects: Equivalent to ++current_.

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constexpr iterator operator++(int) requires forward_range<Base>;

Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;

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constexpr iterator& operator--() requires bidirectional_range<Base>;

Effects: Equivalent to: --current_; return *this;

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constexpr iterator operator--(int) requires bidirectional_range<Base>;

Effects: Equivalent to: auto tmp = *this; --*this; return tmp;

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constexpr iterator& operator+=(difference_type n)
  requires random_access_range<Base>;

Effects: Equivalent to: current_ += n; return *this;

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constexpr iterator& operator-=(difference_type n)
  requires random_access_range<Base>;

Effects: Equivalent to: current_ -= n; return *this;

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friend constexpr bool operator==(const iterator& x, const iterator& y)
  requires equality_comparable<iterator_t<Base>>;

Effects: Equivalent to: return x.current_ == y.current_;

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friend constexpr bool operator<(const iterator& x, const iterator& y)
  requires random_access_range<Base>;

Effects: Equivalent to: return x.current_ < y.current_;

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friend constexpr bool operator>(const iterator& x, const iterator& y)
  requires random_access_range<Base>;

Effects: Equivalent to: return y < x;

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friend constexpr bool operator<=(const iterator& x, const iterator& y)
  requires random_access_range<Base>;

Effects: Equivalent to: return !(y < x);

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friend constexpr bool operator>=(const iterator& x, const iterator& y)
  requires random_access_range<Base>;

Effects: Equivalent to: return !(x < y);

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friend constexpr auto operator<=>(const iterator& x, const iterator& y)
  requires random_access_range<Base> && three_way_comparable<iterator_t<Base>>;

Effects: Equivalent to: return x.current_ <=> y.current_;

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friend constexpr iterator operator+(iterator i, difference_type n)
  requires random_access_range<Base>;
friend constexpr iterator operator+(difference_type n, iterator i)
  requires random_access_range<Base>;

Effects: Equivalent to: return iterator{*i.parent_, i.current_ + n};

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friend constexpr iterator operator-(iterator i, difference_type n)
  requires random_access_range<Base>;

Effects: Equivalent to: return iterator{*i.parent_, i.current_ - n};

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friend constexpr difference_type operator-(const iterator& x, const iterator& y)
  requires sized_sentinel_for<iterator_t<Base>, iterator_t<Base>>;

Effects: Equivalent to: return x.current_ - y.current_;

24.7.7.4 Class template transform_view::sentinel [range.transform.sentinel]

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constexpr explicit sentinel(sentinel_t<Base> end);

Effects: Initializes end_ with end.

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constexpr sentinel(sentinel<!Const> i)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with std::move(i.end_).

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constexpr sentinel_t<Base> base() const;

Effects: Equivalent to: return end_;

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template<bool OtherConst>
  requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);

Effects: Equivalent to: return x.current_ == y.end_;

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template<bool OtherConst>
  requires sized_sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr range_difference_t<maybe-const<OtherConst, V>>
  operator-(const iterator<OtherConst>& x, const sentinel& y);

Effects: Equivalent to: return x.current_ - y.end_;

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template<bool OtherConst>
  requires sized_sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr range_difference_t<maybe-const<OtherConst, V>>
  operator-(const sentinel& y, const iterator<OtherConst>& x);

Effects: Equivalent to: return y.end_ - x.current_;

24.7.8 Take view [range.take]

24.7.8.1 Overview [range.take.overview]

take_view produces a view of the first N elements from another view, or all the elements if the adapted view contains fewer than N.

The name views::take denotes a range adaptor object ([range.adaptor.object]).

Let E and F be expressions, let T be remove_cvref_t<decltype((E))>, and let D be range_difference_t<decltype((E))>.

If decltype((F)) does not model convertible_to<D>, views::take(E, F) is ill-formed.

Otherwise, the expression views::take(E, F) is expression-equivalent to:

(2.1)
If T is a specialization of ranges::empty_view ([range.empty.view]), then ((void) F, decay-copy(E)), except that the evaluations of E and F are indeterminately sequenced.
(2.2)
Otherwise, if T models random_access_range and sized_range and is
- (2.2.1)
 a specialization of span ([views.span]) where T::extent == dynamic_extent,
- (2.2.2)
 a specialization of basic_string_view ([string.view]),
- (2.2.3)
 a specialization of ranges::iota_view ([range.iota.view]), or
- (2.2.4)
 a specialization of ranges::subrange ([range.subrange]),
then T(ranges::begin(E), ranges::begin(E) + min<D>(ranges::size(E), F)), except that E is evaluated only once.
(2.3)
Otherwise, ranges::take_view(E, F).

[Example 1: vector<int> is{0,1,2,3,4,5,6,7,8,9}; for (int i : is | views::take(5)) cout << i << ' '; // prints: 0 1 2 3 4 — end example]

24.7.8.2 Class template take_view [range.take.view]

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namespace std::ranges { template<view V> class take_view : public view_interface<take_view<V>> { private: V base_ = V(); // exposition only range_difference_t<V> count_ = 0; // exposition only // [range.take.sentinel], class template take_view::sentinel template<bool> struct sentinel; // exposition only public: take_view() requires default_initializable<V> = default; constexpr take_view(V base, range_difference_t<V> count); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() requires (!simple-view<V>) { if constexpr (sized_range<V>) { if constexpr (random_access_range<V>) return ranges::begin(base_); else { auto sz = size(); return counted_iterator(ranges::begin(base_), sz); } } else return counted_iterator(ranges::begin(base_), count_); } constexpr auto begin() const requires range<const V> { if constexpr (sized_range<const V>) { if constexpr (random_access_range<const V>) return ranges::begin(base_); else { auto sz = size(); return counted_iterator(ranges::begin(base_), sz); } } else return counted_iterator(ranges::begin(base_), count_); } constexpr auto end() requires (!simple-view<V>) { if constexpr (sized_range<V>) { if constexpr (random_access_range<V>) return ranges::begin(base_) + size(); else return default_sentinel; } else return sentinel<false>{ranges::end(base_)}; } constexpr auto end() const requires range<const V> { if constexpr (sized_range<const V>) { if constexpr (random_access_range<const V>) return ranges::begin(base_) + size(); else return default_sentinel; } else return sentinel<true>{ranges::end(base_)}; } constexpr auto size() requires sized_range<V> { auto n = ranges::size(base_); return ranges::min(n, static_cast<decltype(n)>(count_)); } constexpr auto size() const requires sized_range<const V> { auto n = ranges::size(base_); return ranges::min(n, static_cast<decltype(n)>(count_)); } }; template<class R> take_view(R&&, range_difference_t<R>) -> take_view<views::all_t<R>>; }

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constexpr take_view(V base, range_difference_t<V> count);

Effects: Initializes base_ with std::move(base) and count_ with count.

24.7.8.3 Class template take_view::sentinel [range.take.sentinel]

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namespace std::ranges { template<view V> template<bool Const> class take_view<V>::sentinel { private: using Base = maybe-const<Const, V>; // exposition only template<bool OtherConst> using CI = counted_iterator<iterator_t<maybe-const<OtherConst, V>>>; // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only public: sentinel() = default; constexpr explicit sentinel(sentinel_t<Base> end); constexpr sentinel(sentinel<!Const> s) requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>; constexpr sentinel_t<Base> base() const; friend constexpr bool operator==(const CI<Const>& y, const sentinel& x); template<bool OtherConst = !Const> requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>> friend constexpr bool operator==(const CI<OtherConst>& y, const sentinel& x); }; }

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constexpr explicit sentinel(sentinel_t<Base> end);

Effects: Initializes end_ with end.

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constexpr sentinel(sentinel<!Const> s)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with std::move(s.end_).

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constexpr sentinel_t<Base> base() const;

Effects: Equivalent to: return end_;

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friend constexpr bool operator==(const CI<Const>& y, const sentinel& x);

template<bool OtherConst = !Const>
  requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const CI<OtherConst>& y, const sentinel& x);

Effects: Equivalent to: return y.count() == 0 || y.base() == x.end_;

24.7.9 Take while view [range.take.while]

24.7.9.1 Overview [range.take.while.overview]

Given a unary predicate pred and a view r, take_while_view produces a view of the range [begin(r), ranges::find_if_not(r, pred)).

The name views::take_while denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F, the expression views::take_while(E, F) is expression-equivalent to take_while_view(E, F).

[Example 1: auto input = istringstream{"0 1 2 3 4 5 6 7 8 9"}; auto small = [](const auto x) noexcept { return x < 5; }; auto small_ints = istream_view<int>(input) | views::take_while(small); for (const auto i : small_ints) { cout <> i; cout << i; // prints 6 — end example]

24.7.9.2 Class template take_while_view [range.take.while.view]

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namespace std::ranges { template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> class take_while_view : public view_interface<take_while_view<V, Pred>> { // [range.take.while.sentinel], class template take_while_view::sentinel template<bool> class sentinel; // exposition only V base_ = V(); // exposition only copyable-box<Pred> pred_; // exposition only public: take_while_view() requires default_initializable<V> && default_initializable<Pred> = default; constexpr take_while_view(V base, Pred pred); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr const Pred& pred() const; constexpr auto begin() requires (!simple-view<V>) { return ranges::begin(base_); } constexpr auto begin() const requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>> { return ranges::begin(base_); } constexpr auto end() requires (!simple-view<V>) { return sentinel<false>(ranges::end(base_), addressof(*pred_)); } constexpr auto end() const requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>> { return sentinel<true>(ranges::end(base_), addressof(*pred_)); } }; template<class R, class Pred> take_while_view(R&&, Pred) -> take_while_view<views::all_t<R>, Pred>; }

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constexpr take_while_view(V base, Pred pred);

Effects: Initializes base_ with std::move(base) and pred_ with std::move(pred).

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constexpr const Pred& pred() const;

Effects: Equivalent to: return *pred_;

24.7.9.3 Class template take_while_view::sentinel [range.take.while.sentinel]

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namespace std::ranges { template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> template<bool Const> class take_while_view<V, Pred>::sentinel { // exposition only using Base = maybe-const<Const, V>; // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only const Pred* pred_ = nullptr; // exposition only public: sentinel() = default; constexpr explicit sentinel(sentinel_t<Base> end, const Pred* pred); constexpr sentinel(sentinel<!Const> s) requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>; constexpr sentinel_t<Base> base() const { return end_; } friend constexpr bool operator==(const iterator_t<Base>& x, const sentinel& y); template<bool OtherConst = !Const> requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>> friend constexpr bool operator==(const iterator_t<maybe-const<OtherConst, V>>& x, const sentinel& y); }; }

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constexpr explicit sentinel(sentinel_t<Base> end, const Pred* pred);

Effects: Initializes end_ with end and pred_ with pred.

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constexpr sentinel(sentinel<!Const> s)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with s.end_ and pred_ with s.pred_.

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friend constexpr bool operator==(const iterator_t<Base>& x, const sentinel& y);

template<bool OtherConst = !Const>
  requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const iterator_t<maybe-const<OtherConst, V>>& x,
                                 const sentinel& y);

Effects: Equivalent to: return y.end_ == x || !invoke(*y.pred_, *x);

24.7.10 Drop view [range.drop]

24.7.10.1 Overview [range.drop.overview]

drop_view produces a view excluding the first N elements from another view, or an empty range if the adapted view contains fewer than N elements.

The name views::drop denotes a range adaptor object ([range.adaptor.object]).

Let E and F be expressions, let T be remove_cvref_t<decltype((E))>, and let D be range_difference_t<decltype((E))>.

If decltype((F)) does not model convertible_to<D>, views::drop(E, F) is ill-formed.

Otherwise, the expression views::drop(E, F) is expression-equivalent to:

(2.1)
If T is a specialization of ranges::empty_view ([range.empty.view]), then ((void) F, decay-copy(E)), except that the evaluations of E and F are indeterminately sequenced.
(2.2)
Otherwise, if T models random_access_range and sized_range and is
- (2.2.1)
 a specialization of span ([views.span]) where T::extent == dynamic_extent,
- (2.2.2)
 a specialization of basic_string_view ([string.view]),
- (2.2.3)
 a specialization of ranges::iota_view ([range.iota.view]), or
- (2.2.4)
 a specialization of ranges::subrange ([range.subrange]),
then T(ranges::begin(E) + min<D>(ranges::size(E), F), ranges::end(E)), except that E is evaluated only once.
(2.3)
Otherwise, ranges::drop_view(E, F).

[Example 1: auto ints = views::iota(0) | views::take(10); for (auto i : ints | views::drop(5)) { cout << i << ' '; // prints 5 6 7 8 9 } — end example]

24.7.10.2 Class template drop_view [range.drop.view]

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namespace std::ranges { template<view V> class drop_view : public view_interface<drop_view<V>> { public: drop_view() requires default_initializable<V> = default; constexpr drop_view(V base, range_difference_t<V> count); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() requires (!(simple-view<V> && random_access_range<const V> && sized_range<const V>)); constexpr auto begin() const requires random_access_range<const V> && sized_range<const V>; constexpr auto end() requires (!simple-view<V>) { return ranges::end(base_); } constexpr auto end() const requires range<const V> { return ranges::end(base_); } constexpr auto size() requires sized_range<V> { const auto s = ranges::size(base_); const auto c = static_cast<decltype(s)>(count_); return s < c ? 0 : s - c; } constexpr auto size() const requires sized_range<const V> { const auto s = ranges::size(base_); const auto c = static_cast<decltype(s)>(count_); return s < c ? 0 : s - c; } private: V base_ = V(); // exposition only range_difference_t<V> count_ = 0; // exposition only }; template<class R> drop_view(R&&, range_difference_t<R>) -> drop_view<views::all_t<R>>; }

🔗

constexpr drop_view(V base, range_difference_t<V> count);

Preconditions: count >= 0 is true.

Effects: Initializes base_ with std::move(base) and count_ with count.

🔗

constexpr auto begin()
  requires (!(simple-view<V> &&
              random_access_range<const V> && sized_range<const V>));
constexpr auto begin() const
  requires random_access_range<const V> && sized_range<const V>;

Returns: ranges::next(ranges::begin(base_), count_, ranges::end(base_)).

Remarks: In order to provide the amortized constant-time complexity required by the range concept when drop_view models forward_range, the first overload caches the result within the drop_view for use on subsequent calls.

[Note 1:

Without this, applying a reverse_view over a drop_view would have quadratic iteration complexity.

— end note]

24.7.11 Drop while view [range.drop.while]

24.7.11.1 Overview [range.drop.while.overview]

Given a unary predicate pred and a view r, drop_while_view produces a view of the range [ranges::find_if_not(r, pred), ranges::end(r)).

The name views::drop_while denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F, the expression views::drop_while(E, F) is expression-equivalent to drop_while_view(E, F).

[Example 1: constexpr auto source = " \t \t \t hello there"; auto is_invisible = [](const auto x) { return x == ' ' || x == '\t'; }; auto skip_ws = views::drop_while(source, is_invisible); for (auto c : skip_ws) { cout << c; // prints hello there with no leading space } — end example]

24.7.11.2 Class template drop_while_view [range.drop.while.view]

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namespace std::ranges { template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> class drop_while_view : public view_interface<drop_while_view<V, Pred>> { public: drop_while_view() requires default_initializable<V> && default_initializable<Pred> = default; constexpr drop_while_view(V base, Pred pred); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr const Pred& pred() const; constexpr auto begin(); constexpr auto end() { return ranges::end(base_); } private: V base_ = V(); // exposition only copyable-box<Pred> pred_; // exposition only }; template<class R, class Pred> drop_while_view(R&&, Pred) -> drop_while_view<views::all_t<R>, Pred>; }

🔗

constexpr drop_while_view(V base, Pred pred);

Effects: Initializes base_ with std::move(base) and pred_ with std::move(pred).

🔗

constexpr const Pred& pred() const;

Effects: Equivalent to: return *pred_;

🔗

constexpr auto begin();

Preconditions: pred_.has_value() is true.

Returns: ranges::find_if_not(base_, cref(*pred_)).

Remarks: In order to provide the amortized constant-time complexity required by the range concept when drop_while_view models forward_range, the first call caches the result within the drop_while_view for use on subsequent calls.

[Note 1:

Without this, applying a reverse_view over a drop_while_view would have quadratic iteration complexity.

— end note]

24.7.12 Join view [range.join]

24.7.12.1 Overview [range.join.overview]

join_view flattens a view of ranges into a view .

The name views::join denotes a range adaptor object ([range.adaptor.object]).

Given a subexpression E, the expression views::join(E) is expression-equivalent to join_view<views::all_t<decltype((E))>>{E}.

[Example 1: vector<string> ss{"hello", " ", "world", "!"}; for (char ch : ss | views::join) cout << ch; // prints: hello world! — end example]

24.7.12.2 Class template join_view [range.join.view]

🔗

namespace std::ranges { template<input_range V> requires view<V> && input_range<range_reference_t<V>> class join_view : public view_interface<join_view<V>> { private: using InnerRng = range_reference_t<V>; // exposition only // [range.join.iterator], class template join_view::iterator template<bool Const> struct iterator; // exposition only // [range.join.sentinel], class template join_view::sentinel template<bool Const> struct sentinel; // exposition only V base_ = V(); // exposition only non-propagating-cache<remove_cv_t<InnerRng>> inner_; // exposition only, present only // when !is_reference_v<InnerRng> public: join_view() requires default_initializable<V> = default; constexpr explicit join_view(V base); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() { constexpr bool use_const = simple-view<V> && is_reference_v<range_reference_t<V>>; return iterator<use_const>{*this, ranges::begin(base_)}; } constexpr auto begin() const requires input_range<const V> && is_reference_v<range_reference_t<const V>> { return iterator<true>{*this, ranges::begin(base_)}; } constexpr auto end() { if constexpr (forward_range<V> && is_reference_v<InnerRng> && forward_range<InnerRng> && common_range<V> && common_range<InnerRng>) return iterator<simple-view<V>>{*this, ranges::end(base_)}; else return sentinel<simple-view<V>>{*this}; } constexpr auto end() const requires input_range<const V> && is_reference_v<range_reference_t<const V>> { if constexpr (forward_range<const V> && is_reference_v<range_reference_t<const V>> && forward_range<range_reference_t<const V>> && common_range<const V> && common_range<range_reference_t<const V>>) return iterator<true>{*this, ranges::end(base_)}; else return sentinel<true>{*this}; } }; template<class R> explicit join_view(R&&) -> join_view<views::all_t<R>>; }

🔗

constexpr explicit join_view(V base);

Effects: Initializes base_ with std::move(base).

24.7.12.3 Class template join_view::iterator [range.join.iterator]

🔗

namespace std::ranges { template<input_range V> requires view<V> && input_range<range_reference_t<V>> template<bool Const> struct join_view<V>::iterator { private: using Parent = maybe-const<Const, join_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only using OuterIter = iterator_t<Base>; // exposition only using InnerIter = iterator_t<range_reference_t<Base>>; // exposition only static constexpr bool ref-is-glvalue = // exposition only is_reference_v<range_reference_t<Base>>; OuterIter outer_ = OuterIter(); // exposition only InnerIter inner_ = InnerIter(); // exposition only Parent* parent_ = nullptr; // exposition only constexpr void satisfy(); // exposition only public: using iterator_concept = see below; using iterator_category = see below; // not always present using value_type = range_value_t<range_reference_t<Base>>; using difference_type = see below; iterator() requires default_initializable<OuterIter> && default_initializable<InnerIter> = default; constexpr iterator(Parent& parent, OuterIter outer); constexpr iterator(iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, OuterIter> && convertible_to<iterator_t<InnerRng>, InnerIter>; constexpr decltype(auto) operator*() const { return *inner_; } constexpr InnerIter operator->() const requires has-arrow<InnerIter> && copyable<InnerIter>; constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires ref-is-glvalue && forward_range<Base> && forward_range<range_reference_t<Base>>; constexpr iterator& operator--() requires ref-is-glvalue && bidirectional_range<Base> && bidirectional_range<range_reference_t<Base>> && common_range<range_reference_t<Base>>; constexpr iterator operator--(int) requires ref-is-glvalue && bidirectional_range<Base> && bidirectional_range<range_reference_t<Base>> && common_range<range_reference_t<Base>>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires ref-is-glvalue && equality_comparable<iterator_t<Base>> && equality_comparable<iterator_t<range_reference_t<Base>>>; friend constexpr decltype(auto) iter_move(const iterator& i) noexcept(noexcept(ranges::iter_move(i.inner_))) { return ranges::iter_move(i.inner_); } friend constexpr void iter_swap(const iterator& x, const iterator& y) noexcept(noexcept(ranges::iter_swap(x.inner_, y.inner_))) requires indirectly_swappable<InnerIter>; }; }

iterator::iterator_concept is defined as follows:

(1.1)
If ref-is-glvalue is true and Base and range_reference_t<Base> each model bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
(1.2)
Otherwise, if ref-is-glvalue is true and Base and range_reference_t<Base> each model forward_range, then iterator_concept denotes forward_iterator_tag.
(1.3)
Otherwise, iterator_concept denotes input_iterator_tag.

The member typedef-name iterator_category is defined if and only if ref-is-glvalue is true, Base models forward_range, and range_reference_t<Base> models forward_range .

In that case, iterator::iterator_category is defined as follows:

(2.1)
Let OUTERC denote iterator_traits<iterator_t<Base>>::iterator_category, and let INNERC denote iterator_traits<iterator_t<range_reference_t<Base>>>::iterator_category.
(2.2)
If OUTERC and INNERC each model derived_from<bidirectional_iterator_tag>, iterator_category denotes bidirectional_iterator_tag.
(2.3)
Otherwise, if OUTERC and INNERC each model derived_from<forward_iterator_tag>, iterator_category denotes forward_iterator_tag.
(2.4)
Otherwise, iterator_category denotes input_iterator_tag.

iterator::difference_type denotes the type: common_type_t< range_difference_t<Base>, range_difference_t<range_reference_t<Base>>>

join_view iterators use the satisfy function to skip over empty inner ranges.

🔗

constexpr void satisfy();       // exposition only

Effects: Equivalent to: auto update_inner = [this](const iterator_t<Base>& x) -> auto&& { if constexpr (ref-is-glvalue) // *x is a reference return *x; else return parent_->inner_.emplace-deref(x); }; for (; outer_ != ranges::end(parent_->base_); ++outer_) { auto&& inner = update_inner(outer_); inner_ = ranges::begin(inner); if (inner_ != ranges::end(inner)) return; } if constexpr (ref-is-glvalue) inner_ = InnerIter();

🔗

constexpr iterator(Parent& parent, OuterIter outer);

Effects: Initializes outer_ with std::move(outer) and parent_ with addressof(parent); then calls satisfy().

🔗

constexpr iterator(iterator<!Const> i)
  requires Const &&
           convertible_to<iterator_t<V>, OuterIter> &&
           convertible_to<iterator_t<InnerRng>, InnerIter>;

Effects: Initializes outer_ with std::move(i.outer_), inner_ with std::move(i.inner_), and parent_ with i.parent_.

🔗

constexpr InnerIter operator->() const
  requires has-arrow<InnerIter> && copyable<InnerIter>;

Effects: Equivalent to return inner_;

🔗

constexpr iterator& operator++();

Let inner-range be:

(9.1)
If ref-is-glvalue is true, *outer_.
(9.2)
Otherwise, *parent_->inner_.

Effects: Equivalent to: auto&& inner_rng = inner-range; if (++inner_ == ranges::end(inner_rng)) { ++outer_; satisfy(); } return *this;

🔗

constexpr void operator++(int);

Effects: Equivalent to: ++*this.

🔗

constexpr iterator operator++(int)
  requires ref-is-glvalue && forward_range<Base> &&
           forward_range<range_reference_t<Base>>;

Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;

🔗

constexpr iterator& operator--()
  requires ref-is-glvalue && bidirectional_range<Base> &&
           bidirectional_range<range_reference_t<Base>> &&
           common_range<range_reference_t<Base>>;

Effects: Equivalent to: if (outer_ == ranges::end(parent_->base_)) inner_ = ranges::end(*--outer_); while (inner_ == ranges::begin(*outer_)) inner_ = ranges::end(*--outer_); --inner_; return *this;

🔗

constexpr iterator operator--(int)
  requires ref-is-glvalue && bidirectional_range<Base> &&
           bidirectional_range<range_reference_t<Base>> &&
           common_range<range_reference_t<Base>>;

Effects: Equivalent to: auto tmp = *this; --*this; return tmp;

🔗

friend constexpr bool operator==(const iterator& x, const iterator& y)
  requires ref-is-glvalue && equality_comparable<iterator_t<Base>> &&
           equality_comparable<iterator_t<range_reference_t<Base>>>;

Effects: Equivalent to: return x.outer_ == y.outer_ && x.inner_ == y.inner_;

🔗

friend constexpr void iter_swap(const iterator& x, const iterator& y)
  noexcept(noexcept(ranges::iter_swap(x.inner_, y.inner_)))
  requires indirectly_swappable<InnerIter>;

Effects: Equivalent to: return ranges::iter_swap(x.inner_, y.inner_);

24.7.12.4 Class template join_view::sentinel [range.join.sentinel]

🔗

namespace std::ranges { template<input_range V> requires view<V> && input_range<range_reference_t<V>> template<bool Const> struct join_view<V>::sentinel { private: using Parent = maybe-const<Const, join_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only public: sentinel() = default; constexpr explicit sentinel(Parent& parent); constexpr sentinel(sentinel<!Const> s) requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>; template<bool OtherConst> requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>> friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y); }; }

🔗

constexpr explicit sentinel(Parent& parent);

Effects: Initializes end_ with ranges::end(parent.base_).

🔗

constexpr sentinel(sentinel<!Const> s)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with std::move(s.end_).

🔗

template<bool OtherConst>
  requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);

Effects: Equivalent to: return x.outer_ == y.end_;

24.7.13 Lazy split view [range.lazy.split]

24.7.13.1 Overview [range.lazy.split.overview]

lazy_split_view takes a view and a delimiter, and splits the view into subranges on the delimiter.

The delimiter can be a single element or a view of elements.

The name views::lazy_split denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F, the expression views::lazy_split(E, F) is expression-equivalent to lazy_split_view(E, F).

[Example 1: string str{"the quick brown fox"}; for (auto word : str | views::lazy_split(' ')) { for (char ch : word) cout << ch; cout << '*'; } // The above prints: the*quick*brown*fox* — end example]

24.7.13.2 Class template lazy_split_view [range.lazy.split.view]

🔗

namespace std::ranges { template<auto> struct require-constant; // exposition only template<class R> concept tiny-range = // exposition only sized_range<R> && requires { typename require-constant<remove_reference_t<R>::size()>; } && (remove_reference_t<R>::size() <= 1); template<input_range V, forward_range Pattern> requires view<V> && view<Pattern> && indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> && (forward_range<V> || tiny-range<Pattern>) class lazy_split_view : public view_interface<lazy_split_view<V, Pattern>> { private: V base_ = V(); // exposition only Pattern pattern_ = Pattern(); // exposition only non-propagating-cache<iterator_t<V>> current_; // exposition only, present only // if !forward_range<V> // [range.lazy.split.outer], class template lazy_split_view::outer-iterator template<bool> struct outer-iterator; // exposition only // [range.lazy.split.inner], class template lazy_split_view::inner-iterator template<bool> struct inner-iterator; // exposition only public: lazy_split_view() requires default_initializable<V> && default_initializable<Pattern> = default; constexpr lazy_split_view(V base, Pattern pattern); template<input_range R> requires constructible_from<V, views::all_t<R>> && constructible_from<Pattern, single_view<range_value_t<R>>> constexpr lazy_split_view(R&& r, range_value_t<R> e); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() { if constexpr (forward_range<V>) return outer-iterator<simple-view<V>>{*this, ranges::begin(base_)}; else { current_ = ranges::begin(base_); return outer-iterator<false>{*this}; } } constexpr auto begin() const requires forward_range<V> && forward_range<const V> { return outer-iterator<true>{*this, ranges::begin(base_)}; } constexpr auto end() requires forward_range<V> && common_range<V> { return outer-iterator<simple-view<V>>{*this, ranges::end(base_)}; } constexpr auto end() const { if constexpr (forward_range<V> && forward_range<const V> && common_range<const V>) return outer-iterator<true>{*this, ranges::end(base_)}; else return default_sentinel; } }; template<class R, class P> lazy_split_view(R&&, P&&) -> lazy_split_view<views::all_t<R>, views::all_t>; template<input_range R> lazy_split_view(R&&, range_value_t<R>) -> lazy_split_view<views::all_t<R>, single_view<range_value_t<R>>>; }

🔗

constexpr lazy_split_view(V base, Pattern pattern);

Effects: Initializes base_ with std::move(base), and pattern_ with std::move(pattern).

🔗

template<input_range R>
  requires constructible_from<V, views::all_t<R>> &&
           constructible_from<Pattern, single_view<range_value_t<R>>>
constexpr lazy_split_view(R&& r, range_value_t<R> e);

Effects: Initializes base_ with views::all(std::forward<R>(r)), and pattern_ with views::
single(std::move(e)).

24.7.13.3 Class template lazy_split_view::outer-iterator [range.lazy.split.outer]

🔗

namespace std::ranges { template<input_range V, forward_range Pattern> requires view<V> && view<Pattern> && indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> && (forward_range<V> || tiny-range<Pattern>) template<bool Const> struct lazy_split_view<V, Pattern>::outer-iterator { private: using Parent = maybe-const<Const, lazy_split_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only Parent* parent_ = nullptr; // exposition only iterator_t<Base> current_ = iterator_t<Base>(); // exposition only, present only // if V models forward_range bool trailing_empty_ = false; // exposition only public: using iterator_concept = conditional_t<forward_range<Base>, forward_iterator_tag, input_iterator_tag>; using iterator_category = input_iterator_tag; // present only if Base // models forward_range // [range.lazy.split.outer.value], class lazy_split_view::outer-iterator::value_type struct value_type; using difference_type = range_difference_t<Base>; outer-iterator() = default; constexpr explicit outer-iterator(Parent& parent) requires (!forward_range<Base>); constexpr outer-iterator(Parent& parent, iterator_t<Base> current) requires forward_range<Base>; constexpr outer-iterator(outer-iterator<!Const> i) requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>; constexpr value_type operator*() const; constexpr outer-iterator& operator++(); constexpr decltype(auto) operator++(int) { if constexpr (forward_range<Base>) { auto tmp = *this; ++*this; return tmp; } else ++*this; } friend constexpr bool operator==(const outer-iterator& x, const outer-iterator& y) requires forward_range<Base>; friend constexpr bool operator==(const outer-iterator& x, default_sentinel_t); }; }

Many of the specifications in [range.lazy.split] refer to the notional member current of outer-iterator.

current is equivalent to current_ if V models forward_range, and *parent_->current_ otherwise.

🔗

constexpr explicit outer-iterator(Parent& parent)
  requires (!forward_range<Base>);

Effects: Initializes parent_ with addressof(parent).

24 Ranges library [ranges]

24.1 General [ranges.general]

24.2 Header <ranges> synopsis [ranges.syn]

24.3 Range access [range.access]

24.3.1 General [range.access.general]

24.3.2 ranges​::​begin [range.access.begin]

24.3.3 ranges​::​end [range.access.end]

24.3.4 ranges​::​cbegin [range.access.cbegin]

24.3.5 ranges​::​cend [range.access.cend]

24.3.6 ranges​::​rbegin [range.access.rbegin]

24.3.7 ranges​::​rend [range.access.rend]

24.3.8 ranges​::​crbegin [range.access.crbegin]

24.3.9 ranges​::​crend [range.access.crend]

24.3.10 ranges​::​size [range.prim.size]

24.3.11 ranges​::​ssize [range.prim.ssize]

24.3.12 ranges​::​empty [range.prim.empty]

24.3.13 ranges​::​data [range.prim.data]

24.3.14 ranges​::​cdata [range.prim.cdata]

24.4 Range requirements [range.req]

24.4.1 General [range.req.general]

24.4.2 Ranges [range.range]

24.4.3 Sized ranges [range.sized]

24.4.4 Views [range.view]

24.4.5 Other range refinements [range.refinements]

24.5 Range utilities [range.utility]

24.5.1 General [range.utility.general]

24.5.2 Helper concepts [range.utility.helpers]

24.5.3 View interface [view.interface]

24.5.3.1 General [view.interface.general]

24.5.3.2 Members [view.interface.members]

24.5.4 Sub-ranges [range.subrange]

24.5.4.1 General [range.subrange.general]

24.5.4.2 Constructors and conversions [range.subrange.ctor]

24.5.4.3 Accessors [range.subrange.access]

24.5.5 Dangling iterator handling [range.dangling]

24.6 Range factories [range.factories]

24.6.1 General [range.factories.general]

24.6.2 Empty view [range.empty]

24.6.2.1 Overview [range.empty.overview]

24.6.2.2 Class template empty_­view [range.empty.view]

24.6.3 Single view [range.single]

24.6.3.1 Overview [range.single.overview]

24.6.3.2 Class template single_­view [range.single.view]

24.6.4 Iota view [range.iota]

24.6.4.1 Overview [range.iota.overview]

24.6.4.2 Class template iota_­view [range.iota.view]

24.6.4.3 Class iota_­view​::​iterator [range.iota.iterator]

24.6.4.4 Class iota_­view​::​sentinel [range.iota.sentinel]

24.6.5 Istream view [range.istream]

24.6.5.1 Overview [range.istream.overview]

24.6.5.2 Class template basic_­istream_­view [range.istream.view]

24.6.5.3 Class template basic_­istream_­view​::​iterator [range.istream.iterator]

24.7 Range adaptors [range.adaptors]

24.7.1 General [range.adaptors.general]

24.7.2 Range adaptor objects [range.adaptor.object]

24.7.3 Copyable wrapper [range.copy.wrap]

24.7.4 Non-propagating cache [range.nonprop.cache]

24.7.5 All view [range.all]

24.7.5.1 General [range.all.general]

24.7.5.2 Class template ref_­view [range.ref.view]

24.7.6 Filter view [range.filter]

24.7.6.1 Overview [range.filter.overview]

24.7.6.2 Class template filter_­view [range.filter.view]

24.7.6.3 Class filter_­view​::​iterator [range.filter.iterator]

24.7.6.4 Class filter_­view​::​sentinel [range.filter.sentinel]

24.7.7 Transform view [range.transform]

24.7.7.1 Overview [range.transform.overview]

24.7.7.2 Class template transform_­view [range.transform.view]

24.7.7.3 Class template transform_­view​::​iterator [range.transform.iterator]

24.7.7.4 Class template transform_­view​::​sentinel [range.transform.sentinel]

24.7.8 Take view [range.take]

24.7.8.1 Overview [range.take.overview]

24.7.8.2 Class template take_­view [range.take.view]

24.7.8.3 Class template take_­view​::​sentinel [range.take.sentinel]

24.7.9 Take while view [range.take.while]

24.7.9.1 Overview [range.take.while.overview]

24.7.9.2 Class template take_­while_­view [range.take.while.view]

24.7.9.3 Class template take_­while_­view​::​sentinel [range.take.while.sentinel]

24.7.10 Drop view [range.drop]

24.7.10.1 Overview [range.drop.overview]

24.3.2 ranges::begin [range.access.begin]

24.3.3 ranges::end [range.access.end]

24.3.4 ranges::cbegin [range.access.cbegin]

24.3.5 ranges::cend [range.access.cend]

24.3.6 ranges::rbegin [range.access.rbegin]

24.3.7 ranges::rend [range.access.rend]

24.3.8 ranges::crbegin [range.access.crbegin]

24.3.9 ranges::crend [range.access.crend]

24.3.10 ranges::size [range.prim.size]

24.3.11 ranges::ssize [range.prim.ssize]

24.3.12 ranges::empty [range.prim.empty]

24.3.13 ranges::data [range.prim.data]

24.3.14 ranges::cdata [range.prim.cdata]

24.6.2.2 Class template empty_view [range.empty.view]

24.6.3.2 Class template single_view [range.single.view]

24.6.4.2 Class template iota_view [range.iota.view]

24.6.4.3 Class iota_view::iterator [range.iota.iterator]

24.6.4.4 Class iota_view::sentinel [range.iota.sentinel]

24.6.5.2 Class template basic_istream_view [range.istream.view]

24.6.5.3 Class template basic_istream_view::iterator [range.istream.iterator]

24.7.5.2 Class template ref_view [range.ref.view]

24.7.6.2 Class template filter_view [range.filter.view]

24.7.6.3 Class filter_view::iterator [range.filter.iterator]

24.7.6.4 Class filter_view::sentinel [range.filter.sentinel]

24.7.7.2 Class template transform_view [range.transform.view]

24.7.7.3 Class template transform_view::iterator [range.transform.iterator]

24.7.7.4 Class template transform_view::sentinel [range.transform.sentinel]

24.7.8.2 Class template take_view [range.take.view]

24.7.8.3 Class template take_view::sentinel [range.take.sentinel]

24.7.9.2 Class template take_while_view [range.take.while.view]

24.7.9.3 Class template take_while_view::sentinel [range.take.while.sentinel]

24.7.10.2 Class template drop_view [range.drop.view]

24.7.11.2 Class template drop_while_view [range.drop.while.view]

24.7.12.2 Class template join_view [range.join.view]

24.7.12.3 Class template join_view::iterator [range.join.iterator]

24.7.12.4 Class template join_view::sentinel [range.join.sentinel]

24.7.13.2 Class template lazy_split_view [range.lazy.split.view]

24.7.13.3 Class template lazy_split_view::outer-iterator [range.lazy.split.outer]