Pass by value or pass by reference

emcpp41.cpp

#include <iostream>

struct String
{   
   String()
   {
       
   }
    
   String(const String&)
   {
       std::cout << "    copy" << std::endl;   
   }
    
   String(const String&&)
   {
       std::cout << "    move" << std::endl;   
   }
};

struct ByReference
{
    ByReference(const String& s) : _str(s) {}
    
    String _str;
};

struct ByValue
{
    ByValue(String s) : _str(std::move(s)) {}
    
    String _str;
};

int main()
{
    String s;
    
    std::cout << "Pass by reference:" << std::endl;
    std::cout << "  Contruct form lvalue" << std::endl;
    ByReference c(s);
    std::cout << "  Contruct form rvalue" << std::endl;
    ByReference d(String{});
    
    std::cout << "Pass by value:" << std::endl;
    std::cout << "  Contruct form lvalue" << std::endl;
    ByValue a(s);
    std::cout << "  Contruct form rvalue" << std::endl;
    ByValue b(String{});
    
    return 0;
}