Do identifier rules apply for operator overloading function?

Question

According to the C++ identifier naming rules:

A valid identifier is a sequence of one or more letters, digits, or underscore characters (_) and must start either with a letter or underscore. Spaces, punctuation marks, and symbols cannot be part of an identifier.

But the name of a function for operator overloading can contain characters other than a letter, digit or underscore, like for example:

user_data_type operator+(const user_data_type & t) const;

Is this an exception to the the identifier naming rules or does function names used for operator overloading not considered as an identifier?

Answer 1

operator+ is not a normal identifier, it is an operator-function-id as defined in 13.5/1 in N4140. By definition, it consists of the word operator followed by an operator, the + in your example. By this rule, you can also write

operator +

or even

user_data_type
operator


+
(const user_data_type & t) const;

as again, operator+ is not a normal identifier.

The rule you cite does not apply here.