Some Operators Shouldn’t Be Overloaded

Recall that a few operators guarantee the order in which operands are evaluated. Because using an overloaded operator is really a function call, these guarantees do not apply to overloaded operators. In particular, the operand-evaluation guarantees of the logical AND, logical OR (§ 4.3, p. 141), and comma (§ 4.10, p. 157) operators are not preserved. Moreover, overloaded versions of && or || operators do not preserve short-circuit evaluation properties of the built-in operators. Both operands are always evaluated.

Because the overloaded versions of these operators do not preserve order of evaluation and/or short-circuit evaluation, it is usually a bad idea to overload them. Users are likely to be surprised when the evaluation guarantees they are accustomed to are not honored for code that happens to use an overloaded version of one of these operators.

Another reason not to overload comma, which also applies to the address-of operator, is that unlike most operators, the language defines what the comma and address-of operators mean when applied to objects of class type. Because these operators have built-in meaning, they ordinarily should not be overloaded. Users of the class will be surprised if these operators behave differently from their normal meanings.