12 Overloading [over]

In a function call if the postfix-expression names at least one function or function template, overload resolution is applied as specified in [over.call.func].

If the postfix-expression denotes an object of class type, overload resolution is applied as specified in [over.call.object].

If the postfix-expression is the address of an overload set, overload resolution is applied using that set as described above.

If the function selected by overload resolution is a non-static member function, the program is ill-formed.

Of interest in [over.call.func] are only those function calls in which the postfix-expression ultimately contains an id-expression that denotes one or more functions.

Such a postfix-expression, perhaps nested arbitrarily deep in parentheses, has one of the following forms:

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

In qualified function calls, the function is named by an id-expression preceded by an -> or . operator.

Since the construct A->B is generally equivalent to (*A).B, the rest of [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, [over] assumes that the postfix-expression that is the left operand of the . operator has type “cv T” where T denotes a class.111

The function declarations found by name lookup ([class.member.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 function is named by a primary-expression.

The function declarations found by name lookup ([basic.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 current class is, or is derived from, T, and the keyword this ([expr.prim.this]) refers to it, then the implied object argument is (*this).

Otherwise, a contrived object of type T becomes the implied object argument;112 if overload resolution selects a non-static member function, the call is ill-formed.

If the postfix-expression E in the function call syntax evaluates to a class object of type “cv T”, then the set of candidate functions includes at least the function call operators of T.

The function call operators of T are the results of a search for the name operator() in the scope of T.

In addition, for each non-explicit conversion function declared in T of the form where the optional cv-qualifier-seq is the same cv-qualification as, or a greater cv-qualification than, cv, and where conversion-type-id denotes the type “pointer to function of (${\text{P}}_1,\dots ,{\text{P}}_n$) returning R”, or the type “reference to pointer to function of (${\text{P}}_1,\dots ,{\text{P}}_n$) returning R”, or the type “reference to function of (${\text{P}}_1,\dots ,{\text{P}}_n$) returning R”, a surrogate call function with the unique name call-function and having the form is also considered as a candidate function.

Similarly, surrogate call functions are added to the set of candidate functions for each non-explicit conversion function declared in a base class of T provided the function is not hidden within T by another intervening declaration.113

The argument list submitted to overload resolution consists of the argument expressions present in the function call syntax preceded by the implied object argument (E).