Sams Teach Yourself C++ in One Hour a Day, 9th Edition

Lesson 21

Understanding Function Objects

Function objects, or functors, might sound exotic or intimidating, but they are entities of C++ that you have probably seen, if not also used, without even realizing it.

In this lesson, you learn

• ■   What function objects are

• ■   How to use function objects as predicates

• ■   How unary and binary predicates are implemented using function objects

Function Objects and Predicates

On a conceptual level, function objects are objects that work as functions. On an implementation level, however, function objects are objects of a class that implement operator(). Although functions and function pointers can also be classified as function objects, it is the capability of an object of a class that implements