FreeBSD Manual Pages
std::generator(3) C++ Standard Libary std::generator(3) NAME std::generator - std::generator Synopsis Defined in header <generator> template< class Ref, class V = void, (1) (since C++23) class Allocator = void > class generator : public ranges::view_interface<generator<Ref, V, Allocator>> namespace pmr { template< class Ref, class V = void > using generator = (2) (since C++23) std::generator<Ref, V, std::pmr::polymorphic_allocator<>>; } 1) The class template std::generator presents a view of the elements yielded by the evaluation of a coroutine. 2) Convenience alias template for the generator using the polymor- phic allocator. A std::generator generates a sequence of elements by repeatedly re- suming the coroutine from which it was returned. Each time a co_yield statement is evaluated, the coroutine produces one element of the sequence. When the co_yield statement is of the form co_yield ranges::elements_of(rng), each element of the range rng is successively produced as an element of the sequence. std::generator models view and input_range. The behavior of a program that adds a specialization for std::gener- ator is undefined. Template parameters Ref - the reference type (ranges::range_reference_t) of the generator. If V is void, both the reference type and the value type are in- ferred from Ref V - the value type (range_value_t) of the generator, or void Allocator - an allocator type or void If Allocator is not void, then the behavior is undefined if Alloca- tor does not meet the Allocator requirements. Member types Member type Definition std::conditional_t<std::is_void_v<V>, std::re- move_cvref_t<Ref>, value (private) V>;. (exposition-only member type*) reference std::conditional_t<std::is_void_v<V>, Ref&&, Ref>;. (private) (exposition-only member type*) yielded std::conditional_t<std::is_reference_v<reference>, reference, const reference&>. Type requirements - std::allocator_traits<Allocator>::pointer is a pointer type. - value is a cv-unqualified object type. - reference is either a reference type, or a cv-unqualified object type that models copy_constructible. - Let /*RRef*/ denote:std::remove_reference_t</*reference*/>&&, if /*reference*/ is a reference type, and /*reference*/ otherwise. * std::common_reference_with</*reference*/&&, /*value*/&> is mod- eled. * std::common_reference_with</*reference*/&&, /*RRef*/&&> is mod- eled. * std::common_reference_with</*RRef*/&&, const /*value*/&> is mod- eled. The program is ill-formed if any of these type requirements is not satisfied. Member objects Member name Definition Internally, each active instance of std::generator is associated with a stack (handled as if by object of type std::unique_ptr<std::stack<std::coroutine_handle<>>>). * When begin is called, a new stack is created and the generator is added to the stack. active_ * When co_yield ranges::elements_of(rng) is evaluated in a generator (private) body, rng is converted to a generator and added to the stack that contains the enclosing generator. * When a generator iterator is incremented, the coroutine at the top of the associated stack is resumed. * When a generator finishes (i.e. when final_suspend is called), it is removed from the stack. (exposition-only member object*) coroutine_ a handle of type std::coroutine_handle<promise_type> (private) (exposition-only member object*) Member functions constructor constructs a generator object (public member function) destructor effectively destroys the entire stack of yielded gen- erators (public member function) operator= assigns a generator object (public member function) resumes the initially suspended coroutine and returns an iterator to begin its handle (public member function) end returns std::default_sentinel (public member function) Inherited from std::ranges::view_interface empty returns whether the derived view is empty. Provided if it satisfies (C++20) sized_range or forward_range. (public member function of std::ranges::view_inter- face<D>) cbegin returns a constant iterator to the beginning of the range. (C++23) (public member function of std::ranges::view_inter- face<D>) cend returns a sentinel for the constant iterator of the range. (C++23) (public member function of std::ranges::view_inter- face<D>) operator bool returns whether the derived view is not empty. Pro- vided if (C++20) ranges::empty is applicable to it. (public member function of std::ranges::view_inter- face<D>) Nested classes promise_type the promise type (public member class) iterator the iterator type (exposition-only member class*) Notes Feature-test macro Value Std Feature __cpp_lib_generator 202207L (C++23) std::generator synchronous coroutine generator for ranges Example Can be tried in Compiler Explorer // Run this code #include <generator> #include <iostream> template<typename T> struct Tree { T value; Tree *left{}, *right{}; std::generator<const T&> traverse_inorder() const { if (left) for (const T& x : left->traverse_inorder()) co_yield x; co_yield value; if (right) for (const T& x : right->traverse_inorder()) co_yield x; } }; int main() { Tree<char> tree[] { {'D', tree + 1, tree + 2}, // // // {'B', tree + 3, tree + 4}, {'F', tree + 5, tree + 6}, // // // {'A'}, {'C'}, {'E'}, {'G'} }; for (char x : tree->traverse_inorder()) std::cout << x << ' '; std::cout << '\n'; } Output: A B C D E F G References * C++23 standard (ISO/IEC 14882:2023): * 26.8 Range generators [coro.generator] See also noop_coroutine creates a coroutine handle that has no observable ef- fects when (C++20) resumed or destroyed (function) http://cppreference.com 2024.06.10 std::generator(3)
NAME | Synopsis | Template parameters | Member types | Type requirements | Member objects | Member functions | Notes | Example | Output: | References | See also
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::generator&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>