更新是否应该返回对象？

README.md

@@ -142,6 +142,7 @@ for(decl:col) {
 - [容器1](./modern_C++_30/container1)
 - [容器2](./modern_C++_30/container2)
 - [异常](./modern_C++_30/exception)
+- [是不是应该返回对象？](./modern_C++_30/returnObj)
 
 ### 4.拓展部分
 

modern_C++_30/CMakeLists.txt

@@ -27,3 +27,11 @@ add_executable(relacontainer container2/relacontainer.cpp)
 add_executable(unorder container2/unorder.cpp)
 add_executable(array container2/array.cpp)
 add_executable(exception exception/exception.cpp)
+
+
+add_executable(returnObj returnObj/returnObj1.cpp)
+add_executable(returnObj_add returnObj/returnObj2.cpp)
+add_executable(returnObj3 returnObj/returnObj3.cpp)
+add_executable(returnObj4 returnObj/returnObj4.cpp)
+add_executable(returnObj5 returnObj/returnObj5.cpp)
+add_executable(rvonrvo returnObj/all.cpp)

modern_C++_30/CMakeLists.txt~

@@ -18,3 +18,12 @@ add_executable(forward reference/forward.cpp)
 add_executable(collapses reference/collapses.cpp)
 add_executable(lifetime reference/lifetime.cpp)
 add_executable(dontreturnReference reference/don'treturnReference.cpp)
+
+add_executable(container container1/container.cpp)
+add_executable(cont container2/hash.cpp)
+add_executable(vector_l container1/vector_l.cpp)
+add_executable(priority_queue container2/priority_queue.cpp)
+add_executable(relacontainer container2/relacontainer.cpp)
+add_executable(unorder container2/unorder.cpp)
+add_executable(array container2/array.cpp)
+add_executable(exception exception/exception.cpp)

modern_C++_30/returnObj/all.cpp

@@ -0,0 +1,97 @@
+//
+// Created by light on 19-12-23.
+//
+
+#include <iostream>
+#include <vector>
+#include <string>
+
+struct Test {
+    Test()
+    {
+        //std::cout << "construct a Test object" << std::endl;
+    }
+
+    Test(const Test&)
+    {
+        std::cout << "copy construct  a Test object" << std::endl;
+    }
+
+    Test& operator=(const Test &t)
+    {
+        std::cout << "copy assignment a Test object" << std::endl;
+        return *this;
+    }
+
+    Test(Test&& t)
+    {
+        std::cout << "move construct a Test object" << std::endl;
+    }
+
+    Test& operator=(Test &&t)
+    {
+        std::cout << "move assignment a Test object" << std::endl;
+        return *this;
+    }
+
+    ~Test()
+    {
+        //std::cout << "destruct a Test object" << std::endl;
+    }
+};
+
+Test getTest()
+{
+    // anonymous object
+    return Test();
+}
+
+Test getTestWithName()
+{
+    // named return value
+    Test temp;
+    return temp;
+}
+/**
+ * 1.copy construct本身在RVO和NRVO两种情况下被优化了，如果再加上move反而画蛇添足。
+ * 2.加入了move assignment后，默认是调用move assignment而不是copy assignment，可以将move assignment注释后测试。
+ * 3.对于RVO和NRVO来说，construction的情况编译器优化得比较好了，加入move语义主要是对于assignment有比较大影响
+ */
+int main()
+{
+    std::cout << "==== common case ====" << std::endl;
+    Test o1;
+    std::cout << "---- Test copy construct: " << std::endl;
+    Test o2(o1);  // two ways for copy construct
+    Test o3 = o1;
+    std::cout << "---- Test move construct: " << std::endl;
+    Test o4(std::move(o3));
+    std::cout << "---- Test assignment: " << std::endl;
+    o2 = o1;
+    std::cout << "---- Test move assignment: " << std::endl;
+    Test o5; o5 = std::move(o4);
+
+    std::cout << "\n==== test for rvo ===" << std::endl;
+    std::cout << "---- Test rvo for copy construct: " << std::endl;
+    Test obj11(getTest());
+    Test obj1 = getTest();
+    std::cout << "---- Test rvo for move construct: " << std::endl;
+    Test obj12(std::move(getTest()));
+    std::cout << "---- Test rvo for assignment: " << std::endl;
+    Test obj2; obj2 = getTest();
+    std::cout << "---- Test rvo move assignment: " << std::endl;
+    Test obj5; obj5 = std::move(getTest());
+
+    std::cout << "\n==== test for nrvo ===" << std::endl;
+    std::cout << "---- Test nrvo for copy construct: " << std::endl;
+    Test obj33(getTestWithName());
+    Test obj3 = getTestWithName();
+    std::cout << "---- Test nrvo for move construct: " << std::endl;
+    Test obj34(std::move(getTestWithName()));
+    std::cout << "---- Test nrvo for assignment: " << std::endl;
+    Test obj4; obj4 = getTestWithName();
+    std::cout << "---- Test nrvo move assignment: " << std::endl;
+    Test obj6; obj6 = std::move(getTestWithName());
+
+    return 0;
+}

modern_C++_30/returnObj/returnObj1.cpp

@@ -0,0 +1,49 @@
+//
+// Created by light on 19-12-22.
+//
+
+
+// rvo example
+
+#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;
+    }
+
+};
+
+// 编译器可以优化 返回值移动出去
+A getA_unnamed() {
+    return A();
+}
+
+int main() {
+//    cout<<"构造"<<endl;
+//    auto a = getA_unnamed();
+    cout<<"赋值"<<endl;
+    A aa;
+    aa=getA_unnamed();
+//    aa=std::move(getA_unnamed());
+}

modern_C++_30/returnObj/returnObj2.cpp

@@ -0,0 +1,48 @@
+//
+// Created by light on 19-12-22.
+//
+
+// nrvo example
+
+#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;
+    }
+};
+
+// 编译器可以优化 返回值移动出去
+A getA_named() {
+    A a;
+    return a;
+}
+
+int main() {
+//    cout<<"拷贝"<<endl;
+//    auto a = getA_named();
+
+    cout<<"赋值"<<endl;
+    A aa;
+    aa=getA_named();
+}

modern_C++_30/returnObj/returnObj3.cpp

@@ -0,0 +1,51 @@
+//
+// 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();
+}

modern_C++_30/returnObj/returnObj4.cpp

@@ -0,0 +1,35 @@
+//
+// 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&&)= delete;
+};
+
+A getA_duang() {
+    A a1;
+    A a2;
+    if (rand() > 42) { 
+        return a1; 
+    }
+    else { 
+        return a2; 
+    }
+}
+
+int main() {
+    auto a = getA_duang();
+}

modern_C++_30/returnObj/returnObj5.cpp

@@ -0,0 +1,31 @@
+//
+// 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(const A&&)= delete;
+    A(A&&)= delete;
+};
+
+A getA_unnamed() {
+    return A();
+}
+
+int main() {
+    auto a = getA_unnamed();
+}