book: translate ch03

see #12

code/3/3.5.move.semantics.cpp

@@ -0,0 +1,40 @@
+//
+// 3.5.move.semantics.cpp
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <iostream>
+class A {
+public:
+    int *pointer;
+    A():pointer(new int(1)) { 
+        std::cout << "construct" << pointer << std::endl; 
+    }
+    A(A& a):pointer(new int(*a.pointer)) { 
+        std::cout << "copy" << pointer << std::endl; 
+    } // meaningless object copy
+    A(A&& a):pointer(a.pointer) { 
+        a.pointer = nullptr;
+        std::cout << "move" << pointer << std::endl; 
+    }
+    ~A(){ 
+        std::cout << "destruct" << pointer << std::endl; 
+        delete pointer; 
+    }
+};
+// avoid compiler optimization
+A return_rvalue(bool test) {
+    A a,b;
+    if(test) return a; // equal to static_cast<A&&>(a);
+    else return b;     // equal to static_cast<A&&>(b);
+}
+int main() {
+    A obj = return_rvalue(false);
+    std::cout << "obj:" << std::endl;
+    std::cout << obj.pointer << std::endl;
+    std::cout << *obj.pointer << std::endl;
+    return 0;
+}