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

This header is part of the coroutine support library.

Includes
(C++20)
 Three-way comparison operator support

Classes
(C++20)
 trait type for discovering coroutine promise types
(class template)
(C++20)
 used to refer to a suspended or executing coroutine
(class template)
(C++20)
 hash support for std::coroutine_handle
(class template specialization)
No-op Coroutines
(C++20)
 used for coroutines with no observable effects
(class)
(C++20)
 std::coroutine_handle<std::noop_coroutine_promise>, intended to refer to a no-op coroutine
(typedef)
Trivial Awaitables
(C++20)
 indicates that an await-expression should never suspend
(class)
(C++20)
 indicates that an await-expression should always suspend
(class)

Functions
(C++20)
 compares two coroutine_handle objects
(function)
No-op Coroutines
(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 {}
  };
}

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