PS: There are other advantages to functors, like typedef-ing, or functor organization (I'm thinking "unary_function" etc.)

PS2: In 99&#37; of the cases, the inline cost is actually free, because the functor is nothing more than a wrapper to "operator<".
What is the advantage of functor organization in the case of a class is derived from unary_function ?

In my opinion, functor not just "is nothing more than a wrapper to "operator<". " but normally it is designed as a predicate for looping construct.

Why you say functor is a wrapper for operator< ?

Please comment.