Base

unary_function	Function Object
binary_function	Function Object

The following classes are provided to simplify the typedefs of the argument and result types:

template 
struct unary_function {
    typedef Arg argument_type;
    typedef Result result_type;
};

template 
struct binary_function {
    typedef Arg1 first_argument_type;
    typedef Arg2 second_argument_type;
    typedef Result result_type;
};