94 lines
2.6 KiB
C++
94 lines
2.6 KiB
C++
//
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// Created by light on 19-12-23.
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//
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#include <iostream>
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#include <string>
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#include <vector>
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struct Test {
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Test() {
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// std::cout << "construct a Test object" << std::endl;
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}
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Test(const Test &) {
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std::cout << "copy construct a Test object" << std::endl;
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}
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Test &operator=(const Test &t) {
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std::cout << "copy assignment a Test object" << std::endl;
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return *this;
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}
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Test(Test &&t) { std::cout << "move construct a Test object" << std::endl; }
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Test &operator=(Test &&t) {
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std::cout << "move assignment a Test object" << std::endl;
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return *this;
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}
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~Test() {
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// std::cout << "destruct a Test object" << std::endl;
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}
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};
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Test getTest() {
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// anonymous object
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return Test();
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}
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Test getTestWithName() {
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// named return value
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Test temp;
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return temp;
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}
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/**
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* 1.copy
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* 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。
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* 2.加入了move assignment后，默认是调用move assignment而不是copy
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* assignment，可以将move assignment注释后测试。
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* 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
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*/
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int main() {
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std::cout << "==== common case ====" << std::endl;
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Test o1;
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std::cout << "---- Test copy construct: " << std::endl;
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Test o2(o1); // two ways for copy construct
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Test o3 = o1;
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std::cout << "---- Test move construct: " << std::endl;
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Test o4(std::move(o3));
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std::cout << "---- Test assignment: " << std::endl;
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o2 = o1;
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std::cout << "---- Test move assignment: " << std::endl;
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Test o5;
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o5 = std::move(o4);
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std::cout << "\n==== test for rvo ===" << std::endl;
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std::cout << "---- Test rvo for copy construct: " << std::endl;
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Test obj11(getTest());
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Test obj1 = getTest();
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std::cout << "---- Test rvo for move construct: " << std::endl;
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Test obj12(std::move(getTest()));
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std::cout << "---- Test rvo for assignment: " << std::endl;
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Test obj2;
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obj2 = getTest();
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std::cout << "---- Test rvo move assignment: " << std::endl;
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Test obj5;
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obj5 = std::move(getTest());
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std::cout << "\n==== test for nrvo ===" << std::endl;
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std::cout << "---- Test nrvo for copy construct: " << std::endl;
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Test obj33(getTestWithName());
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Test obj3 = getTestWithName();
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std::cout << "---- Test nrvo for move construct: " << std::endl;
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Test obj34(std::move(getTestWithName()));
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std::cout << "---- Test nrvo for assignment: " << std::endl;
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Test obj4;
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obj4 = getTestWithName();
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std::cout << "---- Test nrvo move assignment: " << std::endl;
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Test obj6;
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obj6 = std::move(getTestWithName());
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return 0;
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}
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