Standard library header <coroutine> (C++20)

 

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Standard library headers

Language support <cfloat> <climits> <compare> (C++20) <contracts> (C++26) <coroutine> (C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint> (C++11) <cstdlib> <exception> <initializer_list> (C++11)   <limits> <new> <source_location> (C++20) <stdfloat> (C++23) <typeinfo> <version> (C++20) Concepts <concepts> (C++20) Diagnostics <cassert> <cerrno> <debugging> (C++26) <stacktrace> (C++23) <stdexcept> <system_error> (C++11) Memory management <memory> <memory_resource> (C++17) <scoped_allocator> (C++11) Metaprogramming <meta> (C++26) <ratio> (C++11) <type_traits> (C++11)

General utilities <any> (C++17) <bitset> <bit> (C++20) <charconv> (C++17) <expected> (C++23) <format> (C++20) <functional> <optional> (C++17) <stdbit.h> (C++26) <tuple> (C++11) <typeindex> (C++11) <utility> <variant> (C++17) Containers <array> (C++11) <deque> <flat_map> (C++23) <flat_set> (C++23) <forward_list> (C++11) <hive> (C++26) <inplace_vector> (C++26)   <list> <map> <mdspan> (C++23) <queue> <set> <span> (C++20) <stack> <unordered_map> (C++11) <unordered_set> (C++11) <vector> Iterators <iterator> Ranges <generator> (C++23) <ranges> (C++20)

Algorithms <algorithm> <numeric> Strings <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> Text processing <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)   Numerics <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <simd> (C++26) <stdckdint.h> (C++26) <valarray> Time <chrono> (C++11) <ctime> C compatibility <ccomplex> (C++11/17/20*) <ciso646> (until C++20) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

Input/output <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) Concurrency support <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) Execution support <execution> (C++17)

 

This header is part of the language support library.

Includes
<compare> (C++20)	Three-way comparison operator support
Classes
coroutine_traits (C++20)	trait type for discovering coroutine promise types (class template)
coroutine_handle (C++20)	used to refer to a suspended or executing coroutine (class template)
std::hash<std::coroutine_handle> (C++20)	hash support for std::coroutine_handle (class template specialization)
No-op Coroutines
noop_coroutine_promise (C++20)	used for coroutines with no observable effects (class)
noop_coroutine_handle (C++20)	std::coroutine_handle<std::noop_coroutine_promise>, intended to refer to a no-op coroutine (typedef)
Trivial Awaitables
suspend_never (C++20)	indicates that an await-expression should never suspend (class)
suspend_always (C++20)	indicates that an await-expression should always suspend (class)
Functions
operator==operator<=> (C++20)	compares two coroutine_handle objects (function)
No-op Coroutines
noop_coroutine (C++20)	creates a coroutine handle that has no observable effects when resumed or destroyed (function)

Synopsis

// all freestanding
#include <compare>

namespace std {
  // coroutine traits
  template<class R, class... ArgTypes> struct coroutine_traits;

  // coroutine handle
  template<class Promise = void> struct coroutine_handle;

  // comparison operators
  constexpr bool operator==(coroutine_handle<> x, coroutine_handle<> y) noexcept;
  constexpr strong_ordering operator<=>(coroutine_handle<> x,
                                        coroutine_handle<> y) noexcept;

  // hash support
  template<class T> struct hash;
  template<class P> struct hash<coroutine_handle<P>>;

  // no-op coroutines
  struct noop_coroutine_promise;

  template<> struct coroutine_handle<noop_coroutine_promise>;
  using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;

  noop_coroutine_handle noop_coroutine() noexcept;

  // trivial awaitables
  struct suspend_never;
  struct suspend_always;
}

Class template std::coroutine_handle

namespace std {
  template<> struct coroutine_handle<void>
  {
    // construct/reset
    constexpr coroutine_handle() noexcept;
    constexpr coroutine_handle(nullptr_t) noexcept;
    coroutine_handle& operator=(nullptr_t) noexcept;

    // export/import
    constexpr void* address() const noexcept;
    static constexpr coroutine_handle from_address(void* addr);

    // observers
    constexpr explicit operator bool() const noexcept;
    bool done() const;

    // resumption
    void operator()() const;
    void resume() const;
    void destroy() const;

  private:
    void* ptr; // exposition-only
  };

  template<class Promise> struct coroutine_handle
  {
    // construct/reset
    constexpr coroutine_handle() noexcept;
    constexpr coroutine_handle(nullptr_t) noexcept;
    static coroutine_handle from_promise(Promise&);
    coroutine_handle& operator=(nullptr_t) noexcept;

    // export/import
    constexpr void* address() const noexcept;
    static constexpr coroutine_handle from_address(void* addr);

    // conversion
    constexpr operator coroutine_handle<>() const noexcept;

    // observers
    constexpr explicit operator bool() const noexcept;
    bool done() const;

    // resumption
    void operator()() const;
    void resume() const;
    void destroy() const;

    // promise access
    Promise& promise() const;

  private:
    void* ptr; // exposition-only
  };
}

Class std::noop_coroutine_promise

namespace std {
  struct noop_coroutine_promise {};
}

Class std::coroutine_handle<std::noop_coroutine_promise>

namespace std {
  template<> struct coroutine_handle<noop_coroutine_promise>
  {
    // conversion
    constexpr operator coroutine_handle<>() const noexcept;

    // observers
    constexpr explicit operator bool() const noexcept;
    constexpr bool done() const noexcept;

    // resumption
    constexpr void operator()() const noexcept;
    constexpr void resume() const noexcept;
    constexpr void destroy() const noexcept;

    // promise access
    noop_coroutine_promise& promise() const noexcept;

    // address
    constexpr void* address() const noexcept;

  private:
    coroutine_handle(/* unspecified */);
    void* ptr; // exposition-only
  };
}

Class std::suspend_never

namespace std {
  struct suspend_never
  {
    constexpr bool await_ready() const noexcept { return true; }
    constexpr void await_suspend(coroutine_handle<>) const noexcept {}
    constexpr void await_resume() const noexcept {}
  };
}

Class std::suspend_always

namespace std {
  struct suspend_always
  {
    constexpr bool await_ready() const noexcept { return false; }
    constexpr void await_suspend(coroutine_handle<>) const noexcept {}
    constexpr void await_resume() const noexcept {}
  };
}