2016-04-29

STL ALGO FUNCTOR

Functors

In <stl_function.h>

SGI STL has defined unary/binary operation templete with traits.

Unary Function

templates

template <class _Arg, class _Result>
struct unary_function {
  typedef _Arg argument_type;
  typedef _Result result_type;
};

Identity, Select

identity is an extensions: it is not part of the standard.

template <class _Tp>
struct _Identity : public unary_function<_Tp,_Tp> {
  const _Tp& operator()(const _Tp& __x) const { return __x; }
};

template <class _Tp> struct identity : public _Identity<_Tp> {};

// select1st and select2nd are extensions: they are not part of the standard.
template <class _Pair>
struct _Select1st : public unary_function<_Pair, typename _Pair::first_type> {
  const typename _Pair::first_type& operator()(const _Pair& __x) const {
    return __x.first;
  }
};

template <class _Pair>
struct _Select2nd : public unary_function<_Pair, typename _Pair::second_type>
{
  const typename _Pair::second_type& operator()(const _Pair& __x) const {
    return __x.second;
  }
};

Binary Function

templates

template <class _Arg1, class _Arg2, class _Result>
struct binary_function {
  typedef _Arg1 first_argument_type;
  typedef _Arg2 second_argument_type;
  typedef _Result result_type;
};

Arithmetic

plus, minus, multipies, divides, modulus, negate

template <class _Tp>
struct plus : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x + __y; }
};

template <class _Tp>
struct minus : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x - __y; }
};

template <class _Tp>
struct multiplies : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x * __y; }
};

template <class _Tp>
struct divides : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x / __y; }
};

template <class _Tp>
struct modulus : public binary_function<_Tp,_Tp,_Tp> 
{
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x % __y; }
};

template <class _Tp>
struct negate : public unary_function<_Tp,_Tp> 
{
  _Tp operator()(const _Tp& __x) const { return -__x; }
};

Relational

equal, not equal, greater, greater equal, less, less equal

template <class _Tp>
struct equal_to : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x == __y; }
};

template <class _Tp>
struct not_equal_to : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x != __y; }
};

template <class _Tp>
struct greater : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x > __y; }
};

template <class _Tp>
struct less : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x < __y; }
};

template <class _Tp>
struct greater_equal : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x >= __y; }
};

template <class _Tp>
struct less_equal : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x <= __y; }
};

Logical

and, or, not. not is unary function.

template <class _Tp>
struct logical_and : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x && __y; }
};

template <class _Tp>
struct logical_or : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x || __y; }
};

template <class _Tp>
struct logical_not : public unary_function<_Tp,bool>
{
  bool operator()(const _Tp& __x) const { return !__x; }
};

Additional

Identity Element

identity_element is not part of the C++ standard.

template <class _Tp> inline _Tp identity_element(plus<_Tp>) {
  return _Tp(0);
}
template <class _Tp> inline _Tp identity_element(multiplies<_Tp>) {
  return _Tp(1);
}

Title:STL ALGO FUNCTOR

Author:_IDLER_

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