From 075c2e089a50d6a2f566d0415c62aa9a6e09f765 Mon Sep 17 00:00:00 2001
From: Glen Fernandes <glen.fernandes@gmail.com>
Date: Wed, 12 Jan 2022 00:58:22 -0500
Subject: [PATCH] Support identity for boost::result_of pre C++11

---
 include/boost/functional/identity.hpp   | 20 ++++++++++++++++
 test/Jamfile.v2                         |  2 ++
 test/identity_result_of_rvalue_test.cpp | 31 +++++++++++++++++++++++++
 test/identity_result_of_test.cpp        | 18 ++++++++++++++
 4 files changed, 71 insertions(+)
 create mode 100644 test/identity_result_of_rvalue_test.cpp
 create mode 100644 test/identity_result_of_test.cpp

diff --git a/include/boost/functional/identity.hpp b/include/boost/functional/identity.hpp
index a4929a9..7021c9b 100644
--- a/include/boost/functional/identity.hpp
+++ b/include/boost/functional/identity.hpp
@@ -34,6 +34,26 @@ struct identity {
         return value;
     }
 #endif
+
+    template<class>
+    struct result { };
+
+    template<class T>
+    struct result<identity(T&)> {
+        typedef T& type;
+    };
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+    template<class T>
+    struct result<identity(T)> {
+        typedef T&& type;
+    };
+
+    template<class T>
+    struct result<identity(T&&)> {
+        typedef T&& type;
+    };
+#endif
 };
 
 } // boost
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 71de379..8767a0b 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -8,4 +8,6 @@ test-suite functional :
     [ run function_test.cpp ]
     [ run identity_test.cpp ]
     [ run identity_rvalue_test.cpp ]
+    [ run identity_result_of_test.cpp ]
+    [ run identity_result_of_rvalue_test.cpp ]
     ;
diff --git a/test/identity_result_of_rvalue_test.cpp b/test/identity_result_of_rvalue_test.cpp
new file mode 100644
index 0000000..48eea5c
--- /dev/null
+++ b/test/identity_result_of_rvalue_test.cpp
@@ -0,0 +1,31 @@
+/*
+Copyright 2022 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include <boost/functional/identity.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/utility/result_of.hpp>
+
+int main()
+{
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(int)>::type,
+        int&&);
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(const int)>::type,
+        int&&);
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(int&&)>::type,
+        int&&);
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(const int&&)>::type,
+        const int&&);
+    return boost::report_errors();
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif
diff --git a/test/identity_result_of_test.cpp b/test/identity_result_of_test.cpp
new file mode 100644
index 0000000..822f522
--- /dev/null
+++ b/test/identity_result_of_test.cpp
@@ -0,0 +1,18 @@
+/*
+Copyright 2022 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#include <boost/functional/identity.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/utility/result_of.hpp>
+
+int main()
+{
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(int&)>::type, int&);
+    BOOST_TEST_TRAIT_SAME(boost::result_of<boost::identity(const int&)>::type,
+        const int&);
+    return boost::report_errors();
+}