std::generator
From cppreference.com
| 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.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.
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.
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.
Data members
| Member | Definition |
active_ (private)
|
Internally, each active instance of
|
coroutine_ (private)
|
a handle of type std::coroutine_handle<promise_type>(exposition-only member object*) |
Member functions
constructs a generator object (public member function) | |
effectively destroys the entire stack of yielded generators (public member function) | |
assigns a generator object (public member function) | |
| resumes the initially suspended coroutine and returns an iterator to its handle (public member function) | |
| returns std::default_sentinel (public member function) | |
Inherited from ranges::view_interface | |
returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range (public member function of std::ranges::view_interface<D>)
| |
(C++23) |
returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>)
|
(C++23) |
returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>)
|
| returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface<D>)
| |
Nested classes
| the promise type (public member class) | |
| 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
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)
co_yield std::ranges::elements_of(left->traverse_inorder());
co_yield value;
if (right)
co_yield std::ranges::elements_of(right->traverse_inorder());
}
};
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 14882:2024):
- 26.8 Range generators [coro.generator]
See also
(C++20) |
creates a coroutine handle that has no observable effects when resumed or destroyed (function) |