From 63589908b5e0ca56860ec5b4d73de8b46770f6c3 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 6 Oct 2024 20:29:27 +0300
Subject: [PATCH] Add sp_type_identity

---
 .../boost/smart_ptr/detail/sp_type_traits.hpp |  7 +++++
 test/Jamfile                                  |  1 +
 test/sp_type_identity_test.cpp                | 31 +++++++++++++++++++
 3 files changed, 39 insertions(+)
 create mode 100644 test/sp_type_identity_test.cpp

diff --git a/include/boost/smart_ptr/detail/sp_type_traits.hpp b/include/boost/smart_ptr/detail/sp_type_traits.hpp
index 6e0dcee..35b702a 100644
--- a/include/boost/smart_ptr/detail/sp_type_traits.hpp
+++ b/include/boost/smart_ptr/detail/sp_type_traits.hpp
@@ -32,6 +32,13 @@ template<class T> struct sp_is_unbounded_array< T[] >: std::true_type
 {
 };
 
+// std::type_identity (C++20)
+
+template<class T> struct sp_type_identity
+{
+    typedef T type;
+};
+
 } // namespace detail
 } // namespace boost
 
diff --git a/test/Jamfile b/test/Jamfile
index 8c67901..c6f0b67 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -427,3 +427,4 @@ run sp_move_only_deleter.cpp ;
 
 run sp_is_bounded_array_test.cpp ;
 run sp_is_unbounded_array_test.cpp ;
+run sp_type_identity_test.cpp ;
diff --git a/test/sp_type_identity_test.cpp b/test/sp_type_identity_test.cpp
new file mode 100644
index 0000000..ed425f0
--- /dev/null
+++ b/test/sp_type_identity_test.cpp
@@ -0,0 +1,31 @@
+// Copyright 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/smart_ptr/detail/sp_type_traits.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+struct X;
+
+int main()
+{
+    using boost::detail::sp_type_identity;
+
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<void>::type, void );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<int>::type, int );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<X>::type, X );
+
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<void const>::type, void const );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<int const>::type, int const );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<X const>::type, X const );
+
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<void(int, X)>::type, void(int, X) );
+
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<int[]>::type, int[] );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<X[]>::type, X[] );
+
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<int[1]>::type, int[1] );
+    BOOST_TEST_TRAIT_SAME( sp_type_identity<X[2]>::type, X[2] );
+
+    return boost::report_errors();
+}