[over.call] (original) (raw)
A function call operator functionis a function named operator()that is a member function with an arbitrary number of parameters.
It may have default arguments.
For an expression of the form
postfix-expression ( expression-list )
where the postfix-expression is of class type, the operator function is selected by overload resolution ([over.call.object]).
If a surrogate call function is selected, let e be the result of invoking the corresponding conversion operator function on the postfix-expression;