When compiling/running this code
#include <iostream>
struct Aok1{
std::string s {"foobar"};
int i{42};
operator std::string (){ return s;} // return by value
};
struct Aok2{
std::string s {"foobar"};
int i{42};
operator const std::string & ()const{ return s;} // const ref
};
struct Ako{
std::string s {"foobar"};
int i{42};
operator std::string & (){ return s;} // non-const ref
};
int main(int argc, char *argv[])
{
{
std::cout << "---------------" << std::endl;
Aok1 a;
std::cout << "first call" << std::endl;
const std::string b = (std::string)a;
std::cout << b << std::endl;
std::cout << "second call" << std::endl;
const std::string c = (std::string)a;
std::cout << c << std::endl;
std::cout << "voila..." << std::endl;
}
{
std::cout << "---------------" << std::endl;
Aok2 a;
std::cout << "first call" << std::endl;
const std::string b = (std::string)a;
std::cout << b << std::endl;
std::cout << "second call" << std::endl;
const std::string c = (std::string)a;
std::cout << c << std::endl;
std::cout << "voila..." << std::endl;
}
{
std::cout << "---------------" << std::endl;
Ako a;
std::cout << "first call" << std::endl;
const std::string b = (std::string)a;
std::cout << b << std::endl;
std::cout << "second call" << std::endl;
const std::string c = (std::string)a;
std::cout << c << std::endl;
std::cout << "voila..." << std::endl;
}
return 0;
}
you will end-up with the following result
---------------
first call
foobar
second call
foobar
voila...
---------------
first call
foobar
second call
foobar
voila...
---------------
first call
foobar
second call
voila...
It seems the compiler is "moving" when a non-const reference cast operator is used here.
This won't happend with gcc, clang or with previous release of intel c++ compiler.
godbolt link : https://godbolt.org/z/xxb74qccM
