awaitable.hpp

// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "../utility/utility.hpp"
#include "../macros.hpp"
#include <coroutine>
#include <type_traits>
 
hi_export_module(hikogui.dispatch.awaitable);
 
hi_export namespace hi::inline v1 {

template<typename T>
concept awaitable = requires(std::remove_reference_t<T>& a, std::coroutine_handle<> b) {
    // clang-format off
    { a.await_ready() } -> std::convertible_to<bool>;
    a.await_suspend(b);
    a.await_resume();
    // clang-format on
};
 
template<typename T>
concept awaitable_with_co_await_member = requires(std::remove_reference_t<T>& a) {
    { a.operator co_await() } -> awaitable;
};
 
template<typename T>
concept awaitable_with_co_await_free_function = requires(std::remove_reference_t<T>& a) {
    { operator co_await(a) } -> awaitable;
};
 
template<typename T>
struct awaitable_cast;
 
template<awaitable T>
struct awaitable_cast<T> {
    template<typename RHS>
    decltype(auto) operator()(RHS&& rhs) const noexcept
    {
        return std::forward<RHS>(rhs);
    }
};
 
template<awaitable_with_co_await_member T>
struct awaitable_cast<T> {
    template<typename RHS>
    decltype(auto) operator()(RHS&& rhs) const noexcept
    {
        return std::forward<RHS>(rhs).operator co_await();
    }
};
 
template<awaitable_with_co_await_free_function T>
struct awaitable_cast<T> {
    template<typename RHS>
    decltype(auto) operator()(RHS&& rhs) const noexcept
    {
        return operator co_await(std::forward<RHS>(rhs));
    }
};

template<typename T>
concept convertible_to_awaitable = requires(std::remove_reference_t<T>& rhs) { awaitable_cast<std::remove_cvref_t<T>>{}(rhs); };

template<awaitable T>
struct await_resume_result {
    using type = decltype(std::declval<T>().await_resume());
};

template<awaitable T>
using await_resume_result_t = await_resume_result<T>::type;
 
} // namespace hi::inline v1