25 Ranges library [ranges]

25.5 Range utilities [range.utility]

25.5.4 Sub-ranges [range.subrange]

25.5.4.2 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.

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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]

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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, static_cast<decltype(size_)>(ranges::size(r))).
(6.2)
Otherwise, subrange(ranges::begin(r), ranges::end(r)).

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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_);