Initial Commit

include/asio/traits/prefer_free.hpp

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+//
+// traits/prefer_free.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_TRAITS_PREFER_FREE_HPP
+#define ASIO_TRAITS_PREFER_FREE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+
+#if defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+# define ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT 1
+#endif // defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace traits {
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_default;
+
+template <typename T, typename Property, typename = void>
+struct prefer_free;
+
+} // namespace traits
+namespace detail {
+
+struct no_prefer_free
+{
+  static constexpr bool is_valid = false;
+  static constexpr bool is_noexcept = false;
+};
+
+#if defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_trait : no_prefer_free
+{
+};
+
+template <typename T, typename Property>
+struct prefer_free_trait<T, Property,
+  void_t<
+    decltype(prefer(declval<T>(), declval<Property>()))
+  >>
+{
+  static constexpr bool is_valid = true;
+
+  using result_type = decltype(
+    prefer(declval<T>(), declval<Property>()));
+
+  static constexpr bool is_noexcept =
+    noexcept(prefer(declval<T>(), declval<Property>()));
+};
+
+#else // defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename Property, typename = void>
+struct prefer_free_trait :
+  conditional_t<
+    is_same<T, decay_t<T>>::value
+      && is_same<Property, decay_t<Property>>::value,
+    no_prefer_free,
+    traits::prefer_free<
+      decay_t<T>,
+      decay_t<Property>>
+  >
+{
+};
+
+#endif // defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+} // namespace detail
+namespace traits {
+
+template <typename T, typename Property, typename>
+struct prefer_free_default :
+  detail::prefer_free_trait<T, Property>
+{
+};
+
+template <typename T, typename Property, typename>
+struct prefer_free :
+  prefer_free_default<T, Property>
+{
+};
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_TRAITS_PREFER_FREE_HPP