Standard Template Library Programmer's Guide

[1] Two different invocations of f may return different results, even if f is called with the same arguments both times. A Binary Function may refer to local state, perform I/O, and so on. The expression f(x,y) is permitted to change f 's state.

Function Object overview, Generator, Unary Function, Adaptable Binary Function

Category: functors

Component type: concept

An Adaptable Generator is a Generator with a nested typedef that defines its result type. [1] This nested typedef makes it possible to use function object adaptors.

Generator

FA type that is a model of Adaptable Generator

None, except for those defined by Generator

The STL does not include any types that are models of Adaptable Generator. An example of a user-defined Adaptable Generator is as follows.

struct counter {

typedef int result_type;

counter() : n(0) {}

result_type operator()() { return n++; }

result_type n;

};

[1] Note the implication of this: a function pointer T (*f)() is a Generator, but not an Adaptable Generator: the expression f::result_type is nonsensical.

Generator, Adaptable Unary Function, Adaptable Binary Function

Category: functors

Component type: concept

An Adaptable Unary Function is a Unary Function with nested typedef s that define its argument type and result type. [1] [2] These nested typedef make it possible to use function object adaptors.

Unary Function

FA type that is a model of Unary Function

None, except for those defined by Unary Function

• negate

• identity

• pointer_to_unary_function

[1] Note the implication of this: a function pointer T (*f)(X) is a Unary Function, but not an Adaptable Unary Function: the expressions f::argument_type and f::result_type are nonsensical.

[2] When you define a class that is a model of Adaptable Unary Function, you must provide these typedef s. The easiest way to do this is to derive the class from the base class unary_function . This is an empty class, with no member functions or member variables; the only reason it exists is to make defining Adaptable Unary Functions more convenient. Unary_function is very similar to the base classes used by the iterator tag functions.

Unary Function, Adaptable Generator, Adaptable Binary Function

Category: functors

Component type: concept

An Adaptable Binary Function is a Binary Function with nested typedef s that define its argument types and result type. [1] [2] These nested typedef s make it possible to use function object adaptors.

Binary Function

FA type that is a model of Binary Function

None, except for those defined by Binary Function

• plus

• project1st

• pointer_to_binary_function

[1] Note the implication of this: a function pointer T (*f)(X,Y) is a Binary Function, but not an Adaptable Binary Function: the expressions f::first_argument_type , f::second_argument_type , and f::result_type are nonsensical.

[2] When you define a class that is a model of Adaptable Binary Function, you must provide these typedef s. The easiest way to do this is to derive the class from the base class binary_function . This is an empty class, with no member functions or member variables; the only reason it exists is to make defining Adaptable Binary Functions more convenient. Binary_function is very similar to the base classes used by the iterator tag functions.

Binary Function, Adaptable Generator, Adaptable Unary Function

Category: functors

Component type: concept

A Predicate is a Unary Function whose result represents the truth or falsehood of some condition. A Predicate might, for example, be a function that takes an argument of type int and returns true if the argument is positive.

Unary Function

FA type that is a model of Predicate

XThe argument type of F

fObject of type F

xObject of type X

• bool (*)(int)