modern-cpp-tutorial/code/3/3.3.rvalue.cpp

//
// 3.3.rvalue.cpp
// modern c++ tutorial
//
// created by changkun at changkun.de
// https://github.com/changkun/modern-cpp-tutorial
//


#include <iostream>
#include <string>

void reference(std::string& str) {
    std::cout << "lvalue" << std::endl;
}
void reference(std::string&& str) {
    std::cout << "rvalue" << std::endl;
}

int main()
{
    std::string  lv1 = "string,";       // lv1 is a lvalue
    // std::string&& r1 = lv1;           // illegal, rvalue can't ref to lvalue
    std::string&& rv1 = std::move(lv1); // legal, std::move can convert lvalue to rvalue
    std::cout << rv1 << std::endl;      // string,
    
    const std::string& lv2 = lv1 + lv1; // legal, const lvalue reference can extend temp variable's lifecycle
    // lv2 += "Test";                   // illegal, const ref can't be modified
    std::cout << lv2 << std::endl;      // string,string
    
    std::string&& rv2 = lv1 + lv2;      // legal, rvalue ref extend lifecycle
    rv2 += "string";                    // legal, non-const reference can be modified
    std::cout << rv2 << std::endl;      // string,string,string,
    
    reference(rv2);                     // output: lvalue
    
    return 0;
}