libcxx/include/__coroutine/noop_coroutine_handle.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H
#define _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H

#include <__config>
#include <__coroutine/coroutine_handle.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CXX20_COROUTINES)

_LIBCPP_BEGIN_NAMESPACE_STD

#if __has_builtin(__builtin_coro_noop)
// [coroutine.noop]
// [coroutine.promise.noop]
struct noop_coroutine_promise {};

// [coroutine.handle.noop]
template <>
struct _LIBCPP_TEMPLATE_VIS coroutine_handle<noop_coroutine_promise> {
public:
    // [coroutine.handle.noop.conv], conversion
    _LIBCPP_HIDE_FROM_ABI
    constexpr operator coroutine_handle<>() const noexcept {
        return coroutine_handle<>::from_address(address());
    }

    // [coroutine.handle.noop.observers], observers
    _LIBCPP_HIDE_FROM_ABI
    constexpr explicit operator bool() const noexcept { return true; }
    _LIBCPP_HIDE_FROM_ABI
    constexpr bool done() const noexcept { return false; }

    // [coroutine.handle.noop.resumption], resumption
    _LIBCPP_HIDE_FROM_ABI
    constexpr void operator()() const noexcept {}
    _LIBCPP_HIDE_FROM_ABI
    constexpr void resume() const noexcept {}
    _LIBCPP_HIDE_FROM_ABI
    constexpr void destroy() const noexcept {}

    // [coroutine.handle.noop.promise], promise access
    _LIBCPP_HIDE_FROM_ABI
    noop_coroutine_promise& promise() const noexcept {
        return *static_cast<noop_coroutine_promise*>(
            __builtin_coro_promise(this->__handle_, alignof(noop_coroutine_promise), false));
    }

    // [coroutine.handle.noop.address], address
    _LIBCPP_HIDE_FROM_ABI
    constexpr void* address() const noexcept { return __handle_; }

private:
    _LIBCPP_HIDE_FROM_ABI
    friend coroutine_handle<noop_coroutine_promise> noop_coroutine() noexcept;

    _LIBCPP_HIDE_FROM_ABI coroutine_handle() noexcept { 
        this->__handle_ = __builtin_coro_noop();
    }

    void* __handle_ = nullptr;
};

using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;

// [coroutine.noop.coroutine]
inline _LIBCPP_HIDE_FROM_ABI
noop_coroutine_handle noop_coroutine() noexcept { return noop_coroutine_handle(); }

#endif // __has_builtin(__builtin_coro_noop)

_LIBCPP_END_NAMESPACE_STD

#endif // __LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CXX20_COROUTINES)

#endif // _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H