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include/asio/uses_executor.hpp

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+//
+// uses_executor.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_USES_EXECUTOR_HPP
+#define ASIO_USES_EXECUTOR_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"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// A special type, similar to std::nothrow_t, used to disambiguate
+/// constructors that accept executor arguments.
+/**
+ * The executor_arg_t struct is an empty structure type used as a unique type
+ * to disambiguate constructor and function overloading. Specifically, some
+ * types have constructors with executor_arg_t as the first argument,
+ * immediately followed by an argument of a type that satisfies the Executor
+ * type requirements.
+ */
+struct executor_arg_t
+{
+  /// Constructor.
+  constexpr executor_arg_t() noexcept
+  {
+  }
+};
+
+/// A special value, similar to std::nothrow, used to disambiguate constructors
+/// that accept executor arguments.
+/**
+ * See asio::executor_arg_t and asio::uses_executor
+ * for more information.
+ */
+ASIO_INLINE_VARIABLE constexpr executor_arg_t executor_arg;
+
+/// The uses_executor trait detects whether a type T has an associated executor
+/// that is convertible from type Executor.
+/**
+ * Meets the BinaryTypeTrait requirements. The Asio library provides a
+ * definition that is derived from false_type. A program may specialize this
+ * template to derive from true_type for a user-defined type T that can be
+ * constructed with an executor, where the first argument of a constructor has
+ * type executor_arg_t and the second argument is convertible from type
+ * Executor.
+ */
+template <typename T, typename Executor>
+struct uses_executor : false_type {};
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_USES_EXECUTOR_HPP