16 Overloading [over]

Of interest in [over.call.func] are only those function calls in which the postfix-expression ultimately contains a name that denotes one or more functions that might be called. Such a postfix-expression, perhaps nested arbitrarily deep in parentheses, has one of the following forms:

postfix-expression:
	postfix-expression . id-expression
	postfix-expression -> id-expression
	primary-expression

These represent two syntactic subcategories of function calls: qualified function calls and unqualified function calls.

In qualified function calls, the name to be resolved is an id-expression and is preceded by an -> or . operator. Since the construct A->B is generally equivalent to (*A).B, the rest of Clause [over] assumes, without loss of generality, that all member function calls have been normalized to the form that uses an object and the . operator. Furthermore, Clause [over] assumes that the postfix-expression that is the left operand of the . operator has type “cv T” where T denotes a class125. Under this assumption, the id-expression in the call is looked up as a member function of T following the rules for looking up names in classes ([class.member.lookup]). The function declarations found by that lookup constitute the set of candidate functions. The argument list is the expression-list in the call augmented by the addition of the left operand of the . operator in the normalized member function call as the implied object argument ([over.match.funcs]).

In unqualified function calls, the name is not qualified by an -> or . operator and has the more general form of a primary-expression. The name is looked up in the context of the function call following the normal rules for name lookup in function calls. The function declarations found by that lookup constitute the set of candidate functions. Because of the rules for name lookup, the set of candidate functions consists (1) entirely of non-member functions or (2) entirely of member functions of some class T. In case (1), the argument list is the same as the expression-list in the call. In case (2), the argument list is the expression-list in the call augmented by the addition of an implied object argument as in a qualified function call. If the keyword this is in scope and refers to class T, or a derived class of T, then the implied object argument is (*this). If the keyword this is not in scope or refers to another class, then a contrived object of type T becomes the implied object argument126. If the argument list is augmented by a contrived object and overload resolution selects one of the non-static member functions of T, the call is ill-formed.