using operator & after class method name

Question

I found the C++ class with API like this:

class foo
{
.....
public:
int& func1() & ;
int func1() && ;
.....
}

what does operator & and && do after the method name and what is the difference between these two function.

Answer 1

These are called "ref qualifiers" and allow you to overload a member function depending on the value category of *this.

• int& func1() & means: this overload of func1 can be invoked on any instance of *this which can be bound to an lvalue reference.

• int func1() && means: this overload of func1 can be invoked on any instance of *this which can be bound to an rvalue reference.

E.g.

foo f; f.func1(); // calls &-qualified version
foo{}.func1();    // calls &&-qualified version