Can the :: operator appear in the context different from scope resolution in qualified name lookup?

Question

As known scope resolution operator used for the purposes of qualified name lookup. But what is the value returned by ::? As I understood it is postfix unary operator. Consider the following:

namespace A
{
    //something
}

A:: //error: expected unqualified-id before ‘int’

int main(){ }

Can you explain that behavior?

Answer 1

The scope resolution operator :: is only a syntatic operator, has no other semantics. That is, there are operators that only contribute to the syntax of the language, and others that contribute to the semantics/runtime behaviour of the program too, and that semantics could be customized. Thats operators overloading.