std::generator
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Range generators
generator
(C++23)
Ranges library
(exposition-only member type*)
(exposition-only member type*)
(exposition-only member object*)
returns a constant iterator to the beginning of the range
(public member function of
returns a sentinel for the constant iterator of the range
(public member function of
creates a coroutine handle that has no observable effects when resumed or destroyed
(function) [edit]
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std::generator
(C++23)
std::generator
Defined in header
<generator>
template<
(1)
(since C++23)
class Ref,
class V = void,
class Allocator = void >
class generator
namespace pmr {
(2)
(since C++23)
template< class Ref, class V = void >
using generator =
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.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.
- std::common_reference_with <
reference&&,value&> is modeled. - std::common_reference_with <
reference&&,RRef&&> is modeled. - std::common_reference_with <
RRef&&, constvalue&> is modeled.
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
beginis 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
resumes the initially suspended coroutine and returns an iterator to its handle
(public member function) [edit]
(public member function) [edit]
Inherited from std::ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies
(public member function of
sized_range or forward_range (public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of
(public member function of
std::ranges::view_interface<D>) [edit]
[edit] Nested classes
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_generator |
202207L |
(C++23) | std::generator – synchronous coroutine generator for ranges
|
[edit] 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
[edit] References
- C++23 standard (ISO/IEC 14882:2024):
- 26.8 Range generators [coro.generator]
[edit] See also
(C++20)
(function) [edit]