An operation of the form op x or x op, where op is an overloadable unary
operator, and x is an expression of
type X, is processed as follows:
?The set of candidate user-defined operators provided by X for the
operation operator op(x) is
determined using the rules of ?4.2.5.
?If the set of candidate user-defined operators is not empty, then this
becomes the set of candidate
operators for the operation. Otherwise, the predefined unary operator op
implementations become the
set of candidate operators for the operation. The predefined
implementations of a given operator are
specified in the description of the operator (?4.5 and ?4.6).
?The overload resolution rules of ?4.4.2 are applied to the set of
candidate operators to select the best
operator with respect to the argument list (x), and this operator becomes
the result of the overload
resolution process. If overload resolution fails to select a single best
operator, a compile-time error
occurs.