support bazel complie this project and format code.

learn_class/modern_cpp_30/obj/obj3.cpp

@@ -0,0 +1,48 @@
+//
+// Created by light on 19-12-22.
+//
+
+#include <iostream>
+
+using namespace std;
+
+// Can copy and move
+class A {
+public:
+  A() { cout << "Create A\n"; }
+
+  ~A() { cout << "Destroy A\n"; }
+
+  A(const A &) { cout << "Copy A\n"; }
+
+  A(A &&) { cout << "Move A\n"; }
+
+  A &operator=(const A &a) {
+    std::cout << "copy assignment" << std::endl;
+    return *this;
+  }
+
+  A &operator=(A &&a) {
+    cout << "move assignment\n";
+    return *this;
+  }
+};
+// 编译器无法优化
+A getA_duang() {
+  A a1;
+  A a2;
+  if (rand() > 42) {
+    return a1;
+  } else {
+    return a2;
+  }
+}
+
+int main() {
+  //    cout<<"拷贝"<<endl;
+  //    auto a = getA_duang();
+
+  cout << "赋值" << endl;
+  A aa;
+  aa = getA_duang();
+}