Question

Consider this code:

#include <iostream>


void f(int&& i)
{
    std::cout << "f(int&&)\n";
}

void f(const int&& i)
{
    std::cout << "f(const int&&)\n";
}


int fun_i()
{
    return 0;
}

const int fun_ci()
{
    return 0;
}

int main()
{
    f(fun_i());
    f(fun_ci());
}

If I compile this with MSVC 2012, the output is:

f(int&&)
f(const int&&)

If I compile with GCC 4.7, the output is:

f(int&&)
f(int&&)

Which is correct?

(If I remove the second definition of f, the program will not compile under MSVC 2012, but it does compile under GCC 4.7.)

Answer 1

GCC is correct. From paragraph 4 of 3.10 Lvalues and rvalues [basic.lval]:

Class prvalues can have cv-qualified types; non-class prvalues always have cv-unqualified types. […]

A function call such as fun_ci() is in fact a prvalue*, and as such has type int, not const int. int&& is a better match than const int&&, and should be picked by overload resolution.

*: it’s customarily said that top-level cv-qualifiers are ignored for non-class return types.