async_traits.hpp

Go to the documentation of this file.

 
#pragma once
 
#include <concepts>
#include <type_traits>
#include <utility>
 
namespace uni20::async
{
 
template <typename T> class Async;
 
template <typename T> struct async_value_type
{
    using type = T;
};
 
template <typename T> struct async_value_type<Async<T>>
{
    using type = T;
};
 
template <typename T> using async_value_t = typename async_value_type<std::remove_cvref_t<T>>::type;
 
namespace detail
{
 
template <typename T, typename = void> struct default_is_async_alias : std::false_type
{};
 
template <typename T>
struct default_is_async_alias<T, std::void_t<typename std::remove_cvref_t<T>::async_alias_tag>> : std::true_type
{};
 
} // namespace detail
 
template <typename T> struct is_async_alias : detail::default_is_async_alias<std::remove_cvref_t<T>>
{};
 
template <typename T> inline constexpr bool is_async_alias_v = is_async_alias<std::remove_cvref_t<T>>::value;
 
namespace detail
{
 
// Poison ordinary lookup so only an ADL-visible write-through operation can
// make an alias assignable.
void assign_through() = delete;
 
template <typename Target, typename Source>
concept async_alias_assignable_from = is_async_alias_v<Target> && requires(Target& target, Source&& source) {
  { assign_through(target, std::forward<Source>(source)) } -> std::same_as<void>;
};
 
template <typename Target, typename Source>
concept async_alias_assignment_source = async_alias_assignable_from<Target, async_value_t<Source> const&>;
 
template <typename Target, typename Source>
  requires async_alias_assignable_from<Target, Source>
void assign_async_alias(Target& target, Source&& source)
{
  assign_through(target, std::forward<Source>(source));
}
 
} // namespace detail
} // namespace uni20::async