Implement boost::exchange

include/boost/core/exchange.hpp

@@ -0,0 +1,47 @@
+/*
+Copyright 2018 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#ifndef BOOST_CORE_EXCHANGE_HPP
+#define BOOST_CORE_EXCHANGE_HPP
+
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include <utility>
+#endif
+
+namespace boost {
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+template<class T, class U = T>
+BOOST_CXX14_CONSTEXPR inline T exchange(T& t, U&& u)
+{
+    T v = std::move(t);
+    t = std::forward<U>(u);
+    return v;
+}
+#else
+namespace detail {
+
+template<class T>
+struct exchanger {
+    typedef T type;
+};
+
+} /* detail */
+
+template<class T>
+inline T exchange(T& t, const typename detail::exchanger<T>::type& u)
+{
+    T v = t;
+    t = u;
+    return v;
+}
+#endif
+
+} /* boost */
+
+#endif