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std::generator

From cppreference.com
< cpp‎ | coroutine
 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Coroutine support
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(C++20)
Coroutine handle
(C++20)
No-op coroutines
(C++20)
(C++20)
Trivial awaitables
(C++20)
(C++20)
Range generators
generator
(C++23)
 
Ranges library
Range adaptors
 
std::generator
 
Defined in header <generator>
template<

    class Ref,
    class V = void,
    class Allocator = void >
class generator

    : public ranges::view_interface<generator<Ref, V, Allocator>>
 (1) (since C++23)
namespace pmr {

    template< class Ref, class V = void >
    using generator =
        std::generator<Ref, V, std::pmr::polymorphic_allocator<>>;

}
 (2) (since C++23)
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 polymorphic allocator.

A std::generator generates a sequence of elements by repeatedly resuming 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::generator is undefined.

Contents

[edit] 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 inferred from Ref
V - the value type (ranges::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 Allocator does not meet the Allocator requirements.

[edit] Member types

Member Definition
value (private) std::conditional_t<std::is_void_v<V>, std::remove_cvref_t<Ref>, V>;
(exposition-only member type*)
reference (private) std::conditional_t<std::is_void_v<V>, Ref&&, Ref>;
(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.

The program is ill-formed if any of these type requirements is not satisfied.

[edit] Data members

Member Definition
active_ (private)

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.
  • When co_yield ranges::elements_of(rng) is evaluated in a generator 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 promise_type::final_suspend is called), it is removed from the stack.
    (exposition-only member object*)
coroutine_ (private) a handle of type std::coroutine_handle<promise_type>
(exposition-only member object*)

[edit] Member functions

 constructs a generator object
(public member function) [edit]
effectively destroys the entire stack of yielded generators
(public member function) [edit]
assigns a generator object
(public member function)