Simplify exchange implementation for pre-C++11

include/boost/core/exchange.hpp

@@ -15,18 +15,10 @@ Distributed under the Boost Software License, Version 1.0.
 #endif
 
 namespace boost {
-namespace detail {
-
-template<class T>
-struct exchange_type {
-    typedef T type;
-};
-
-} /* detail */
 
 #if defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
-template<class T>
+template<class T, class U>
-inline T exchange(T& t, const typename detail::exchange_type<T>::type& u)
+inline T exchange(T& t, const U& u)
 {
     T v = t;
     t = u;
@@ -34,19 +26,11 @@ inline T exchange(T& t, const typename detail::exchange_type<T>::type& u)
 }
 #else
 #if BOOST_WORKAROUND(BOOST_MSVC, < 1800)
-template<class T>
+template<class T, class U>
-inline T exchange(T& t, const typename detail::exchange_type<T>::type& u)
+inline T exchange(T& t, U&& u)
 {
     T v = std::move(t);
-    t = u;
+    t = std::forward<U>(u);
-    return v;
-}
-
-template<class T>
-inline T exchange(T& t, typename detail::exchange_type<T>::type&& u)
-{
-    T v = std::move(t);
-    t = std::move(u);
     return v;
 }
 #else

test/exchange_move_test.cpp

@@ -59,10 +59,37 @@ void test2()
     BOOST_TEST(x.i() == 2);
 }
 
+class C3 {
+public:
+    explicit C3(int i)
+        : i_(i) { }
+    C3(C3&& c)
+        : i_(c.i_) { }
+    C3& operator=(C1&& c) {
+        i_ = c.i();
+        return *this;
+    }
+    int i() const {
+        return i_;
+    }
+private:
+    C3(const C3&);
+    C3& operator=(const C3&);
+    int i_;
+};
+
+void test3()
+{
+    C3 x(1);
+    BOOST_TEST(boost::exchange(x, C1(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
 int main()
 {
     test1();
     test2();
+    test3();
     return boost::report_errors();
 }
 #else

test/exchange_test.cpp

@@ -56,10 +56,36 @@ void test3()
     BOOST_TEST(x.i() == 2);
 }
 
+class C3 {
+public:
+    explicit C3(int i)
+        : i_(i) { }
+    C3(const C3& c)
+        : i_(c.i_) { }
+    C3& operator=(const C1& c) {
+        i_ = c.i();
+        return *this;
+    }
+    int i() const {
+        return i_;
+    }
+private:
+    C3& operator=(const C3&);
+    int i_;
+};
+
+void test4()
+{
+    C3 x(1);
+    BOOST_TEST(boost::exchange(x, C1(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
 int main()
 {
     test1();
     test2();
     test3();
+    test4();
     return boost::report_errors();
 }