std::generator<Ref,V,Allocator>::promise_type::yield_value

 

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std::generator

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generator::generator

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generator::begin

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promise_type

generator::promise_type::get_return_object

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generator::promise_type::final_suspend

generator::promise_type::yield_value

generator::promise_type::return_void

generator::promise_type::unhandled_exception

generator::promise_type::operator new

generator::promise_type::operator delete

Iterator

generator::iterator::iterator

generator::iterator::operator=

generator::iterator::operator*

generator::iterator::operator++ generator::iterator::operator++(int)

operator==(generator::iterator, std::default_sentinel_t)

 

std::suspend_always yield_value( yielded val ) noexcept;	(1)	(since C++23)
auto yield_value( const std::remove_reference_t<yielded>& lval )     requires std::is_rvalue_reference_v<yielded> &&              std::constructible_from<std::remove_cvref_t<yielded>,                  const std::remove_reference_t<yielded>&>;	(2)	(since C++23)
template< class R2, class V2, class Alloc2, class Unused >     requires std::same_as<typename std::generator<T2, V2, Alloc2>::yielded,                           yielded> auto yield_value( ranges::elements_of<std::generator<T2, V2, Alloc2>&&,                                       Unused> g ) noexcept;	(3)	(since C++23)
template< class R2, class V2, class Alloc2, class Unused >     requires std::same_as<typename std::generator<T2, V2, Alloc2>::yielded,                           yielded> auto yield_value( ranges::elements_of<std::generator<T2, V2, Alloc2>&,                                       Unused> g ) noexcept;	(4)	(since C++23)
template< ranges::input_range R, class Alloc >     requires std::convertible_to<ranges::range_reference_t<R>, yielded> auto yield_value( ranges::elements_of<R, Alloc> r );	(5)	(since C++23)

An implementation of coroutine interface functions used internally to support operator co_yield.

(yielded is a reference type defined in std::generator.)

1) Assigns std::addressof(val) to value_. Returns {}.

2) Returns an awaitable object x of an unspecified type that stores an object of type std::remove_cvref_t<yielded>. x is direct-non-list-initialized with lval, whose member functions are configured so that value_ points to that stored object. Then suspends the coroutine.

3, 4) Let x be some generator object.

Returns an awaitable object of an unspecified type 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

• std::rethrow_exception(except_) if bool(except_) is true.
• If bool(except_) is false, the await_resume member has no effects.

The coroutine referred to by g.range.coroutine_ must be suspended at its initial suspend point. Otherwise the behavior is undefined.

5) Equivalent to:

auto nested = [](std::allocator_arg_t, Alloc, ranges::iterator_t<R> i,
                 ranges::sentinel_t<R> s) ->
    std::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))));

2,3) A handle referring to the coroutine whose promise object is *this must be at the top of *active_ of some generator object. Otherwise, the behavior is undefined.

2-5) A yield-expression that calls these overload has the type void.

Parameters

val	-	a value which is a result of the yield-expression evaluation
lval	-	an lvalue which is a result of the yield-expression evaluation
g	-	a range of elements produced by a generator
r	-	a range of elements

Return value

1) The awaitable object of type std::suspend_always.

2-5) An awaitable object of an unspecified type as described above.

Exceptions

2,5) May throw any exception thrown by the initialization of the stored object.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3899	C++23	yield_value on a range of elements produced by lvalue generator used generic elements_of overload	used special elements_of overload for such generators
LWG 4119	C++23	range_value_t in generator's template argument as part of the return type of nested in (5) may be ill-formed	used void