How to solve ambiguity caused by function overloading like this?

Question

I have a piece of code similar to this:

#include <iostream>

using namespace std;

template<typename T>
class Class
{
public:
    Class() {}
    void foo(T)  {cout << "foo(T) is called \n";}
    void foo(T&) {cout << "foo(T&) is called \n";}
};

int main()
{
    Class<int> c;
    int a = 1;

    c.foo(1);
    c.foo(a);

    return 0;
}

I want to have both overloads of function foo because foo(T&) is more efficient but I can't use a literal constant as it's argument and foo(T) will work for literal constants although it is not as efficient as foo(T&). But when I define both functions there will be an ambiguous call when c.foo(a) is going to execute.

error: call of overloaded 'foo(int&)' is ambiguous

How can I overcome this problem?

Answer 1

You can pass by const reference const T& so that it will also accept literal constants, or pass by rvalue reference T&& instead of T so that it will only accept rvalues (like literal constants)