Simplify exchange implementation for pre-C++11

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();
 }