When do you use function objects in C++?

Question

I see function objects used often together with STL algorithms. Did function objects came about because of these algorithms? When do you use a function object in C++? What is its benefits?

Answer 1

The idea of encapsulating a function as an object dates back to Lisp and Smalltalk. The C++ idea of functor was a chapter in Jim Coplien's book Advanced C++ Programming Styles and Idioms in 1991. STL used the idiom and further popularized it.