C++ Primer, Fifth Edition

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 ...