Parametric Polymorphism and References

fjl (2)
I get the feeling that this is a bad idea in C++, but before I abandon trying to make it work and go back to pointers and dereferencing (which work just fine) I though I'd ask. The idea here is to have an overloaded function taking references to various types, and here's a demonstration of it not working:

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#include <iostream>

void gimmi(int &x)
 {
     x = 42;
 }
void gimmi(int x)
 {
     std::cout << x;
 }
 
int main()
{
    int i=123;
    int &j = i;
    
    gimmi(j);           // Fails - ambiguous
    gimmi((int &)j);    // Fails - ambiguous
    gimmi((int &)i);    // Fails - ambiguous
    gimmi(i);           // Fails - ambiguous

    gimmi((int)i);      // Okay, except on Microsoft(?!?)
    gimmi(456);         // Okay

    return 0;
}

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Basically, once you've defined gimmi(int &x) *and* gimmi(int x) you have to cast to get it to disambiguate; but nothing I've tried allows me to cast to match gimmi(int &x). All attempts are still considered by the compilers as ambiguous. (I've tested this on gcc 10.2, gcc 5.9.4, clang 10.0.1, MSVC 19.28, ICC 18)

Any ideas what's going on? I don't need a solution - pointers work - but I'd like to know if this can be made to as well, or am I flogging a dead horse?
Last edited on
JLBorges (13770)
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void gimmi( int& ) { std::cout << "gimmi( lvalue reference to int )\n" ; }
void gimmi( const int& ) { std::cout << "gimmi( lvalue reference to const int )\n" ; }
void gimmi( int&& ) { std::cout << "gimmi( rvalue reference to int )\n" ; }

int main()
{
    int i = 23 ;
    const int j = 44 ;

    gimmi(i) ; // gimmi( lvalue reference to int )
    gimmi(j) ; // gimmi( lvalue reference to const int )
    gimmi(+i) ; // gimmi( rvalue reference to int )
}
fjl (2)
Perfect, thanks! Other replies I've had elsewhere were along the lines of "but why do you want to do it". Do you, perchance, have chapter and verse on it?
JLBorges (13770)
> Do you, perchance, have chapter and verse on it?

The gory details are here:
Draft Standard: https://eel.is/c++draft/over
cppreference: https://en.cppreference.com/w/cpp/language/overload_resolution

The writeup on this page, specific to this particular question, may be easier to digest:
http://thbecker.net/articles/rvalue_references/section_03.html
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