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include/asio/detail/utility.hpp

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+//
+// detail/utility.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_DETAIL_UTILITY_HPP
+#define ASIO_DETAIL_UTILITY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <utility>
+
+namespace asio {
+namespace detail {
+
+#if defined(ASIO_HAS_STD_INDEX_SEQUENCE)
+
+using std::index_sequence;
+using std::index_sequence_for;
+using std::make_index_sequence;
+
+#else // defined(ASIO_HAS_STD_INDEX_SEQUENCE)
+
+template <std::size_t...>
+struct index_sequence
+{
+};
+
+template <typename T, typename U>
+struct join_index_sequences;
+
+template <std::size_t... I, std::size_t... J>
+struct join_index_sequences<index_sequence<I...>, index_sequence<J...>>
+{
+  using type = index_sequence<I..., J...>;
+};
+
+template <std::size_t First, std::size_t Last>
+struct index_pack :
+  join_index_sequences<
+    typename index_pack<First, First + (Last - First + 1) / 2 - 1>::type,
+    typename index_pack<First + (Last - First + 1) / 2, Last>::type
+  >
+{
+};
+
+template <std::size_t N>
+struct index_pack<N, N>
+{
+  using type = index_sequence<N>;
+};
+
+template <std::size_t Begin, std::size_t End>
+struct index_range : index_pack<Begin, End - 1>
+{
+};
+
+template <std::size_t N>
+struct index_range<N, N>
+{
+  using type = index_sequence<>;
+};
+
+template <typename... T>
+using index_sequence_for = typename index_range<0, sizeof...(T)>::type;
+
+template <std::size_t N>
+using make_index_sequence = typename index_range<0, N>::type;
+
+#endif // defined(ASIO_HAS_STD_INDEX_SEQUENCE)
+
+} // namespace detail
+} // namespace asio
+
+#endif // ASIO_DETAIL_UTILITY_HPP