Move identity to core

include/boost/functional/identity.hpp

@@ -8,54 +8,10 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_FUNCTIONAL_IDENTITY_HPP
 #define BOOST_FUNCTIONAL_IDENTITY_HPP
 
-#include <boost/config.hpp>
-#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
-#include <utility>
-#endif
-
-namespace boost {
-
-struct identity {
-    typedef void is_transparent;
-
-#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
-    template<class T>
-    BOOST_CONSTEXPR T&& operator()(T&& value) const BOOST_NOEXCEPT {
-        return std::forward<T>(value);
-    }
-#else
-    template<class T>
-    BOOST_CONSTEXPR const T& operator()(const T& value) const BOOST_NOEXCEPT {
-        return value;
-    }
-
-    template<class T>
-    BOOST_CONSTEXPR T& operator()(T& value) const BOOST_NOEXCEPT {
-        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
+/*
+The header file at this path is deprecated;
+use <boost/core/identity.hpp> instead.
+*/
+#include <boost/core/identity.hpp>
 
 #endif