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

 

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Standard Library headers

Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.

Language Support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11)   <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error> (C++11)
General utilities
<utility> <memory> <memory_resource> (C++17) <scoped_allocator> (C++11)   <expected> (C++23)	<bitset> <tuple> (C++11) <optional> (C++17) <any> (C++17)	<variant> (C++17) <type_traits> (C++11) <ratio> (C++11) <chrono> (C++11)	<typeindex> (C++11) <functional> <stacktrace> (C++23) <ctime>
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<string> <string_view> (C++17) <cstring>	<charconv> (C++17) <format> (C++20)	<cctype> <cwctype>	<cwchar> <cuchar> (C++11)
Localization
<locale> <clocale>	<codecvt> (C++11/17)
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<span> (C++20) <array> (C++11) <vector>	<deque> <forward_list> (C++11) <list>	<map> <set> <queue>	<unordered_map> (C++11) <unordered_set> (C++11) <stack>
Iterators
<iterator>
Ranges
<ranges> (C++20)
Algorithms
<algorithm>	<execution> (C++17)
Numerics
<complex> <random> (C++11)	<valarray> <numeric>	<bit> (C++20) <numbers> (C++20)	<cfenv> (C++11) <cmath>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<syncstream> (C++20) <spanstream> (C++23) <sstream> <fstream>	<cstdio> <cinttypes> (C++11) <strstream> (C++98/)
Regular expressions
<regex> (C++11)
Filesystem support
<filesystem> (C++17)
Thread support
<thread> (C++11) <atomic> (C++11) <mutex> (C++11)	<shared_mutex> (C++14) <condition_variable> (C++11)   <future> (C++11)	<stop_token> (C++20) <semaphore> (C++20)	<latch> (C++20) <barrier> (C++20)
C compatibility
<cstdbool> (C++11/17/20) <ccomplex> (C++11/17/20)	<ctgmath> (C++11/17/20) <cstdalign> (C++11/17/20)	<ciso646> (until C++20) <stdatomic.h>

 

This header is part of the coroutine 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

#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 {}
  };
}