25 Ranges library [ranges]

25.8 Range generators [coro.generator]

25.8.5 Class generator​::​promise_type [coro.generator.promise]

namespace std { template<class Ref, class Val, class Allocator> class generator<Ref, Val, Allocator>::promise_type { public: generator get_return_object() noexcept; suspend_always initial_suspend() const noexcept { return {}; } auto final_suspend() noexcept; suspend_always yield_value(yielded val) noexcept; auto yield_value(const remove_reference_t<yielded>& lval) requires is_rvalue_reference_v<yielded> && constructible_from<remove_cvref_t<yielded>, const remove_reference_t<yielded>&>; template<class R2, class V2, class Alloc2, class Unused> requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded> auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&&, Unused> g) noexcept; template<class R2, class V2, class Alloc2, class Unused> requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded> auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&, Unused> g) noexcept; template<ranges::input_range R, class Alloc> requires convertible_to<ranges::range_reference_t<R>, yielded> auto yield_value(ranges::elements_of<R, Alloc> r); void await_transform() = delete; void return_void() const noexcept {} void unhandled_exception(); void* operator new(size_t size) requires same_as<Allocator, void> || default_initializable<Allocator>; template<class Alloc, class... Args> void* operator new(size_t size, allocator_arg_t, const Alloc& alloc, const Args&...); template<class This, class Alloc, class... Args> void* operator new(size_t size, const This&, allocator_arg_t, const Alloc& alloc, const Args&...); void operator delete(void* pointer, size_t size) noexcept; private: add_pointer_t<yielded> value_ = nullptr; // exposition only exception_ptr except_; // exposition only }; }
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generator get_return_object() noexcept;
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Returns: A generator object whose member coroutine_ is coroutine_handle<promise_type>​::​​from_promise(*this), and whose member active_ points to an empty stack.
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auto final_suspend() noexcept;
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Preconditions: A handle referring to the coroutine whose promise object is *this is at the top of *active_ of some generator object x.
This function is called by that coroutine upon reaching its final suspend point ([dcl.fct.def.coroutine]).
3
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Returns: An awaitable object of unspecified type ([expr.await]) whose member functions arrange for the calling coroutine to be suspended, pop the coroutine handle from the top of *x.active_, and resume execution of the coroutine referred to by x.active_->top() if *x.active_ is not empty.
If it is empty, control flow returns to the current coroutine caller or resumer ([dcl.fct.def.coroutine]).
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suspend_always yield_value(yielded val) noexcept;
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Effects: Equivalent to value_ = addressof(val).
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Returns: {}.
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auto yield_value(const remove_reference_t<yielded>& lval) requires is_rvalue_reference_v<yielded> && constructible_from<remove_cvref_t<yielded>, const remove_reference_t<yielded>&>;
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Preconditions: A handle referring to the coroutine whose promise object is *this is at the top of *active_ of some generator object.
7
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Returns: An awaitable object of an unspecified type ([expr.await]) that stores an object of type remove_cvref_t<yielded> direct-non-list-initialized with lval, whose member functions arrange for value_ to point to that stored object and then suspend the coroutine.
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Throws: Any exception thrown by the initialization of the stored object.
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Remarks: A yield-expression that calls this function has type void ([expr.yield]).
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template<class R2, class V2, class Alloc2, class Unused> requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded> auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&&, Unused> g) noexcept; template<class R2, class V2, class Alloc2, class Unused> requires same_as<typename generator<R2, V2, Alloc2>::yielded, yielded> auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&, Unused> g) noexcept;
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Preconditions: A handle referring to the coroutine whose promise object is *this is at the top of *active_ of some generator object x.
The coroutine referred to by g.range.coroutine_ is suspended at its initial suspend point.
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Returns: An awaitable object of an unspecified type ([expr.await]) into which g.range is moved, whose member await_ready returns false, whose member await_suspend pushes g.range.coroutine_ into *x.active_ and resumes execution of the coroutine referred to by g.range.​coroutine_, and whose member await_resume evaluates rethrow_exception(except_) if bool(except_) is true.
If bool(except_) is false, the await_resume member has no effects.
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Remarks: A yield-expression that calls one of these functions has type void ([expr.yield]).
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template<ranges::input_range R, class Alloc> requires convertible_to<ranges::range_reference_t<R>, yielded> auto yield_value(ranges::elements_of<R, Alloc> r);
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Effects: Equivalent to: auto nested = [](allocator_arg_t, Alloc, ranges::iterator_t<R> i, ranges::sentinel_t<R> s) -> generator<yielded, void, Alloc> { for (; i != s; ++i) { co_yield static_cast<yielded>(*i); } }; return yield_value(ranges::elements_of(nested( allocator_arg, r.allocator, ranges::begin(r.range), ranges::end(r.range))));
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[Note 1: 
A yield-expression that calls this function has type void ([expr.yield]).
— end note]
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void unhandled_exception();
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Preconditions: A handle referring to the coroutine whose promise object is *this is at the top of *active_ of some generator object x.
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Effects: If the handle referring to the coroutine whose promise object is *this is the sole element of *x.active_, equivalent to throw, otherwise, assigns current_exception() to except_.
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void* operator new(size_t size) requires same_as<Allocator, void> || default_initializable<Allocator>; template<class Alloc, class... Args> void* operator new(size_t size, allocator_arg_t, const Alloc& alloc, const Args&...); template<class This, class Alloc, class... Args> void* operator new(size_t size, const This&, allocator_arg_t, const Alloc& alloc, const Args&...);
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Let A be
  • (17.1)
    Allocator, if it is not void,
  • (17.2)
    Alloc for the overloads with a template parameter Alloc, or
  • (17.3)
    allocator<void> otherwise.
Let B be allocator_traits<A>​::​template rebind_alloc<U> where U is an unspecified type whose size and alignment are both __STDCPP_DEFAULT_NEW_ALIGNMENT__.
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Mandates: allocator_traits<B>​::​pointer is a pointer type.
For the overloads with a template parameter Alloc, same_as<Allocator, void> || convertible_to<const Alloc&, Allocator> is modeled.
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Effects: Initializes an allocator b of type B with A(alloc), for the overloads with a function parameter alloc, and with A() otherwise.
Uses b to allocate storage for the smallest array of U sufficient to provide storage for a coroutine state of size size, and unspecified additional state necessary to ensure that operator delete can later deallocate this memory block with an allocator equal to b.
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Returns: A pointer to the allocated storage.
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void operator delete(void* pointer, size_t size) noexcept;
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Preconditions: pointer was returned from an invocation of one of the above overloads of operator new with a size argument equal to size.
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Effects: Deallocates the storage pointed to by pointer using an allocator equivalent to that used to allocate it.