Added type_identity forwarding header.

include/boost/iterator/detail/type_traits/type_identity.hpp

@@ -0,0 +1,54 @@
+/*
+ * 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)
+ *
+ * Copyright (c) 2025 Andrey Semashev
+ */
+/*!
+ * \file iterator/detail/type_traits/type_identity.hpp
+ *
+ * This header contains definition of \c negation type trait.
+ */
+
+#ifndef BOOST_ITERATOR_DETAIL_TYPE_TRAITS_TYPE_IDENTITY_HPP_INCLUDED_
+#define BOOST_ITERATOR_DETAIL_TYPE_TRAITS_TYPE_IDENTITY_HPP_INCLUDED_
+
+#include <type_traits>
+#include <boost/config.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+#if (defined(__cpp_lib_type_identity) && (__cpp_lib_type_identity >= 201806l)) || \
+    /* Note: MSVC 19.21 does not define _MSVC_LANG to 202002 in c++latest (C++20) mode but to a value larger than 201703 */ \
+    (defined(BOOST_MSSTL_VERSION) && (BOOST_MSSTL_VERSION >= 142) && (_MSC_VER >= 1921) && (BOOST_CXX_VERSION > 201703l))
+
+namespace boost {
+namespace iterators {
+namespace detail {
+
+using std::type_identity;
+
+} // namespace detail
+} // namespace iterator
+} // namespace boost
+
+#else
+
+#include <boost/type_traits/type_identity.hpp>
+
+namespace boost {
+namespace iterators {
+namespace detail {
+
+using boost::type_identity;
+
+} // namespace detail
+} // namespace iterator
+} // namespace boost
+
+#endif
+
+#endif // BOOST_ITERATOR_DETAIL_TYPE_TRAITS_TYPE_IDENTITY_HPP_INCLUDED_