gcc/libstdc++-v3/include/bits/stl_function.h

// Functor implementations -*- C++ -*-

// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996-1998
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file stl_function.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef __SGI_STL_INTERNAL_FUNCTION_H
#define __SGI_STL_INTERNAL_FUNCTION_H

namespace std
{
// 20.3.1 base classes
/** @defgroup s20_3_1_base Functor Base Classes
 *  Function objects, or @e functors, are objects with an @c operator()
 *  defined and accessible.  They can be passed as arguments to algorithm
 *  templates and used in place of a function pointer.  Not only is the
 *  resulting expressiveness of the library increased, but the generated
 *  code can be more efficient than what you might write by hand.  When we
 *  refer to "functors," then, generally we include function pointers in
 *  the description as well.
 *
 *  Often, functors are only created as temporaries passed to algorithm
 *  calls, rather than being created as named variables.
 *
 *  Two examples taken from the standard itself follow.  To perform a
 *  by-element addition of two vectors @c a and @c b containing @c double,
 *  and put the result in @c a, use
 *  \code
 *  transform (a.begin(), a.end(), b.begin(), a.begin(), plus<double>());
 *  \endcode
 *  To negate every element in @c a, use
 *  \code
 *  transform(a.begin(), a.end(), a.begin(), negate<double>());
 *  \endcode
 *  The addition and negation functions will be inlined directly.
 *
 *  The standard functiors are derived from structs named @c unary_function
 *  and @c binary_function.  These two classes contain nothing but typedefs,
 *  to aid in generic (template) programming.  If you write your own
 *  functors, you might consider doing the same.
 *
 *  @{
*/
/**
 *  This is one of the @link s20_3_1_base functor base classes@endlink.
*/
template <class _Arg, class _Result>
struct unary_function {
  typedef _Arg argument_type;   ///< @c argument_type is the type of the argument (no surprises here)
  typedef _Result result_type;  ///< @c result_type is the return type
};

/**
 *  This is one of the @link s20_3_1_base functor base classes@endlink.
*/
template <class _Arg1, class _Arg2, class _Result>
struct binary_function {
  typedef _Arg1 first_argument_type;   ///< the type of the first argument (no surprises here)
  typedef _Arg2 second_argument_type;  ///< the type of the second argument
  typedef _Result result_type;         ///< type of the return type
};      
/** @}  */

// 20.3.2 arithmetic
/** @defgroup s20_3_2_arithmetic Arithmetic Classes
 *  Because basic math often needs to be done during an algorithm, the library
 *  provides functors for those operations.  See the documentation for
 *  @link s20_3_1_base the base classes@endlink for examples of their use.
 *
 *  @{
*/
/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct plus : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x + __y; }
};

/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct minus : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x - __y; }
};

/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct multiplies : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x * __y; }
};

/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct divides : public binary_function<_Tp,_Tp,_Tp> {
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x / __y; }
};

/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct modulus : public binary_function<_Tp,_Tp,_Tp> 
{
  _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x % __y; }
};

/// One of the @link s20_3_2_arithmetic math functors@endlink.
template <class _Tp>
struct negate : public unary_function<_Tp,_Tp> 
{
  _Tp operator()(const _Tp& __x) const { return -__x; }
};
/** @}  */

/** The @c identity_element functions are not part of the C++ standard; SGI
 *  provided them as an extension.  Its argument is an operation, and its
 *  return value is the identity element for that operation.  It is overloaded
 *  for addition and multiplication, and you can overload it for your own
 *  nefarious operations.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Tp> inline _Tp identity_element(plus<_Tp>) {
  return _Tp(0);
}
/// An \link SGIextensions SGI extension \endlink.
template <class _Tp> inline _Tp identity_element(multiplies<_Tp>) {
  return _Tp(1);
}
/** @}  */

// 20.3.3 comparisons
/** @defgroup s20_3_3_comparisons Comparison Classes
 *  The library provides six wrapper functors for all the basic comparisons
 *  in C++, like @c <.
 *
 *  @{
*/
/// One of the @link s20_3_3_comparisons comparison functors@endlink.
template <class _Tp>
struct equal_to : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x == __y; }
};

/// One of the @link s20_3_3_comparisons comparison functors@endlink.
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; }
};

/// One of the @link s20_3_3_comparisons comparison functors@endlink.
template <class _Tp>
struct greater : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x > __y; }
};

/// One of the @link s20_3_3_comparisons comparison functors@endlink.
template <class _Tp>
struct less : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x < __y; }
};

/// One of the @link s20_3_3_comparisons comparison functors@endlink.
template <class _Tp>
struct greater_equal : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x >= __y; }
};

/// One of the @link s20_3_3_comparisons comparison functors@endlink.
template <class _Tp>
struct less_equal : public binary_function<_Tp,_Tp,bool> 
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x <= __y; }
};
/** @}  */

// 20.3.4 logical operations
/** @defgroup s20_3_4_logical Boolean Operations Classes
 *  Here are wrapper functors for Boolean operations:  @c &&, @c ||, and @c !.
 *
 *  @{
*/
/// One of the @link s20_3_4_logical Boolean operations functors@endlink.
template <class _Tp>
struct logical_and : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x && __y; }
};

/// One of the @link s20_3_4_logical Boolean operations functors@endlink.
template <class _Tp>
struct logical_or : public binary_function<_Tp,_Tp,bool>
{
  bool operator()(const _Tp& __x, const _Tp& __y) const { return __x || __y; }
};

/// One of the @link s20_3_4_logical Boolean operations functors@endlink.
template <class _Tp>
struct logical_not : public unary_function<_Tp,bool>
{
  bool operator()(const _Tp& __x) const { return !__x; }
};
/** @}  */

// 20.3.5 negators
/** @defgroup s20_3_5_negators Negators
 *  The functions @c not1 and @c not2 each take a predicate functor
 *  and return an instance of @c unary_negate or
 *  @c binary_negate, respectively.  These classes are functors whose
 *  @c operator() performs the stored predicate function and then returns
 *  the negation of the result.
 *
 *  For example, given a vector of integers and a trivial predicate,
 *  \code
 *  struct IntGreaterThanThree
 *    : public std::unary_function<int, bool>
 *  {
 *      bool operator() (int x) { return x > 3; }
 *  };
 *  
 *  std::find_if (v.begin(), v.end(), not1(IntGreaterThanThree()));
 *  \endcode
 *  The call to @c find_if will locate the first index (i) of @c v for which
 *  "!(v[i] > 3)" is true.
 *
 *  The not1/unary_negate combination works on predicates taking a single
 *  argument.  The not2/binary_negate combination works on predicates which
 *  take two arguments.
 *
 *  @{
*/
/// One of the @link s20_3_5_negators negation functors@endlink.
template <class _Predicate>
class unary_negate
  : public unary_function<typename _Predicate::argument_type, bool> {
protected:
  _Predicate _M_pred;
public:
  explicit unary_negate(const _Predicate& __x) : _M_pred(__x) {}
  bool operator()(const typename _Predicate::argument_type& __x) const {
    return !_M_pred(__x);
  }
};

/// One of the @link s20_3_5_negators negation functors@endlink.
template <class _Predicate>
inline unary_negate<_Predicate> 
not1(const _Predicate& __pred)
{
  return unary_negate<_Predicate>(__pred);
}

/// One of the @link s20_3_5_negators negation functors@endlink.
template <class _Predicate> 
class binary_negate 
  : public binary_function<typename _Predicate::first_argument_type,
                           typename _Predicate::second_argument_type,
                           bool> {
protected:
  _Predicate _M_pred;
public:
  explicit binary_negate(const _Predicate& __x) : _M_pred(__x) {}
  bool operator()(const typename _Predicate::first_argument_type& __x, 
                  const typename _Predicate::second_argument_type& __y) const
  {
    return !_M_pred(__x, __y); 
  }
};

/// One of the @link s20_3_5_negators negation functors@endlink.
template <class _Predicate>
inline binary_negate<_Predicate> 
not2(const _Predicate& __pred)
{
  return binary_negate<_Predicate>(__pred);
}
/** @}  */

// 20.3.6 binders
/** @defgroup s20_3_6_binder Binder Classes
 *  Binders turn functions/functors with two arguments into functors with
 *  a single argument, storing an argument to be applied later.  For
 *  example, an variable @c B of type @c binder1st is constructed from a functor
 *  @c f and an argument @c x.  Later, B's @c operator() is called with a
 *  single argument @c y.  The return value is the value of @c f(x,y).
 *  @c B can be "called" with various arguments (y1, y2, ...) and will in
 *  turn call @c f(x,y1), @c f(x,y2), ...
 *
 *  The function @c bind1st is provided to save some typing.  It takes the
 *  function and an argument as parameters, and returns an instance of
 *  @c binder1st.
 *
 *  The type @c binder2nd and its creator function @c bind2nd do the same
 *  thing, but the stored argument is passed as the second parameter instead
 *  of the first, e.g., @c bind2nd(std::minus<float>,1.3) will create a
 *  functor whose @c operator() accepts a floating-point number, subtracts
 *  1.3 from it, and returns the result.  (If @c bind1st had been used,
 *  the functor would perform "1.3 - x" instead.
 *
 *  Creator-wrapper functions like @c bind1st are intended to be used in
 *  calling algorithms.  Their return values will be temporary objects.
 *  (The goal is to not require you to type names like
 *  @c std::binder1st<std::plus<int>> for declaring a variable to hold the
 *  return value from @c bind1st(std::plus<int>,5).
 *
 *  These become more useful when combined with the composition functions.
 *
 *  @{
*/
/// One of the @link s20_3_6_binder binder functors@endlink.
template <class _Operation> 
class binder1st
  : public unary_function<typename _Operation::second_argument_type,
                          typename _Operation::result_type> {
protected:
  _Operation op;
  typename _Operation::first_argument_type value;
public:
  binder1st(const _Operation& __x,
            const typename _Operation::first_argument_type& __y)
      : op(__x), value(__y) {}
  typename _Operation::result_type
  operator()(const typename _Operation::second_argument_type& __x) const {
    return op(value, __x); 
  }
#ifdef _GLIBCPP_RESOLVE_LIB_DEFECTS
  //109.  Missing binders for non-const sequence elements
  typename _Operation::result_type
  operator()(typename _Operation::second_argument_type& __x) const {
    return op(value, __x); 
  }
#endif
};

/// One of the @link s20_3_6_binder binder functors@endlink.
template <class _Operation, class _Tp>
inline binder1st<_Operation> 
bind1st(const _Operation& __fn, const _Tp& __x) 
{
  typedef typename _Operation::first_argument_type _Arg1_type;
  return binder1st<_Operation>(__fn, _Arg1_type(__x));
}

/// One of the @link s20_3_6_binder binder functors@endlink.
template <class _Operation> 
class binder2nd
  : public unary_function<typename _Operation::first_argument_type,
                          typename _Operation::result_type> {
protected:
  _Operation op;
  typename _Operation::second_argument_type value;
public:
  binder2nd(const _Operation& __x,
            const typename _Operation::second_argument_type& __y) 
      : op(__x), value(__y) {}
  typename _Operation::result_type
  operator()(const typename _Operation::first_argument_type& __x) const {
    return op(__x, value); 
  }
#ifdef _GLIBCPP_RESOLVE_LIB_DEFECTS
  //109.  Missing binders for non-const sequence elements
  typename _Operation::result_type
  operator()(typename _Operation::first_argument_type& __x) const {
    return op(__x, value); 
  }
#endif
};

/// One of the @link s20_3_6_binder binder functors@endlink.
template <class _Operation, class _Tp>
inline binder2nd<_Operation> 
bind2nd(const _Operation& __fn, const _Tp& __x) 
{
  typedef typename _Operation::second_argument_type _Arg2_type;
  return binder2nd<_Operation>(__fn, _Arg2_type(__x));
}
/** @}  */

/** As an extension to the binders, SGI provided composition functors and
 *  wrapper functions to aid in their creation.  The @c unary_compose
 *  functor is constructed from two functions/functors, @c f and @c g.
 *  Calling @c operator() with a single argument @c x returns @c f(g(x)).
 *  The function @c compose1 takes the two functions and constructs a
 *  @c unary_compose variable for you.
 *  
 *  @c binary_compose is constructed from three functors, @c f, @c g1,
 *  and @c g2.  Its @c operator() returns @c f(g1(x),g2(x)).  The function
 *  @compose2 takes f, g1, and g2, and constructs the @c binary_compose
 *  instance for you.  For example, if @c f returns an int, then
 *  \code
 *  int answer = (compose2(f,g1,g2))(x);
 *  \endcode
 *  is equivalent to
 *  \code
 *  int temp1 = g1(x);
 *  int temp2 = g2(x);
 *  int answer = f(temp1,temp2);
 *  \endcode
 *  But the first form is more compact, and can be passed around as a
 *  functor to other algorithms.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2>
class unary_compose
  : public unary_function<typename _Operation2::argument_type,
                          typename _Operation1::result_type> 
{
protected:
  _Operation1 _M_fn1;
  _Operation2 _M_fn2;
public:
  unary_compose(const _Operation1& __x, const _Operation2& __y) 
    : _M_fn1(__x), _M_fn2(__y) {}
  typename _Operation1::result_type
  operator()(const typename _Operation2::argument_type& __x) const {
    return _M_fn1(_M_fn2(__x));
  }
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2>
inline unary_compose<_Operation1,_Operation2> 
compose1(const _Operation1& __fn1, const _Operation2& __fn2)
{
  return unary_compose<_Operation1,_Operation2>(__fn1, __fn2);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2, class _Operation3>
class binary_compose
  : public unary_function<typename _Operation2::argument_type,
                          typename _Operation1::result_type> {
protected:
  _Operation1 _M_fn1;
  _Operation2 _M_fn2;
  _Operation3 _M_fn3;
public:
  binary_compose(const _Operation1& __x, const _Operation2& __y, 
                 const _Operation3& __z) 
    : _M_fn1(__x), _M_fn2(__y), _M_fn3(__z) { }
  typename _Operation1::result_type
  operator()(const typename _Operation2::argument_type& __x) const {
    return _M_fn1(_M_fn2(__x), _M_fn3(__x));
  }
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2, class _Operation3>
inline binary_compose<_Operation1, _Operation2, _Operation3> 
compose2(const _Operation1& __fn1, const _Operation2& __fn2, 
         const _Operation3& __fn3)
{
  return binary_compose<_Operation1,_Operation2,_Operation3>
    (__fn1, __fn2, __fn3);
}
/** @}  */

// 20.3.7 adaptors pointers functions
/** @defgroup s20_3_7_adaptors Adaptors for pointers to functions
 *  The advantage of function objects over pointers to functions is that
 *  the objects in the standard library declare nested typedefs describing
 *  their argument and result types with uniform names (e.g., @c result_type
 *  from the base classes @c unary_function and @c binary_function).
 *  Sometimes those typedefs are required, not just optional.
 *
 *  Adaptors are provided to turn pointers to unary (single-argument) and
 *  binary (double-argument) functions into function objects.  The long-winded
 *  functor @c pointer_to_unary_function is constructed with a function
 *  pointer @c f, and its @c operator() called with argument @c x returns
 *  @c f(x).  The functor @c pointer_to_binary_function does the same thing,
 *  but with a double-argument @c f and @c operator().
 *
 *  The function @c ptr_fun takes a pointer-to-function @c f and constructs
 *  an instance of the appropriate functor.
 *
 *  @{
*/
/// One of the @link s20_3_7_adaptors adaptors for function pointers@endlink.
template <class _Arg, class _Result>
class pointer_to_unary_function : public unary_function<_Arg, _Result> {
protected:
  _Result (*_M_ptr)(_Arg);
public:
  pointer_to_unary_function() {}
  explicit pointer_to_unary_function(_Result (*__x)(_Arg)) : _M_ptr(__x) {}
  _Result operator()(_Arg __x) const { return _M_ptr(__x); }
};

/// One of the @link s20_3_7_adaptors adaptors for function pointers@endlink.
template <class _Arg, class _Result>
inline pointer_to_unary_function<_Arg, _Result> ptr_fun(_Result (*__x)(_Arg))
{
  return pointer_to_unary_function<_Arg, _Result>(__x);
}

/// One of the @link s20_3_7_adaptors adaptors for function pointers@endlink.
template <class _Arg1, class _Arg2, class _Result>
class pointer_to_binary_function : 
  public binary_function<_Arg1,_Arg2,_Result> {
protected:
    _Result (*_M_ptr)(_Arg1, _Arg2);
public:
    pointer_to_binary_function() {}
    explicit pointer_to_binary_function(_Result (*__x)(_Arg1, _Arg2)) 
      : _M_ptr(__x) {}
    _Result operator()(_Arg1 __x, _Arg2 __y) const {
      return _M_ptr(__x, __y);
    }
};

/// One of the @link s20_3_7_adaptors adaptors for function pointers@endlink.
template <class _Arg1, class _Arg2, class _Result>
inline pointer_to_binary_function<_Arg1,_Arg2,_Result> 
ptr_fun(_Result (*__x)(_Arg1, _Arg2)) {
  return pointer_to_binary_function<_Arg1,_Arg2,_Result>(__x);
}
/** @}  */


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

/** As an extension, SGI provided a functor called @c identity.  When a
 *  functor is required but no operations are desired, this can be used as a
 *  pass-through.  Its @c operator() returns its argument unchanged.
 *
 *  @addtogroup SGIextensions
*/
template <class _Tp> struct identity : public _Identity<_Tp> {};

// extension documented next
template <class _Pair>
struct _Select1st : public unary_function<_Pair, typename _Pair::first_type> {
  typename _Pair::first_type& operator()(_Pair& __x) const {
    return __x.first;
  }
  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>
{
  typename _Pair::second_type& operator()(_Pair& __x) const {
    return __x.second;
  }
  const typename _Pair::second_type& operator()(const _Pair& __x) const {
    return __x.second;
  }
};

/** @c select1st and @c select2nd are extensions provided by SGI.  Their
 *  @c operator()s
 *  take a @c std::pair as an argument, and return either the first member
 *  or the second member, respectively.  They can be used (especially with
 *  the composition functors) to "strip" data from a sequence before
 *  performing the remainder of an algorithm.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Pair> struct select1st : public _Select1st<_Pair> {};
/// An \link SGIextensions SGI extension \endlink.
template <class _Pair> struct select2nd : public _Select2nd<_Pair> {};
/** @}  */

// extension documented next
template <class _Arg1, class _Arg2>
struct _Project1st : public binary_function<_Arg1, _Arg2, _Arg1> {
  _Arg1 operator()(const _Arg1& __x, const _Arg2&) const { return __x; }
};

template <class _Arg1, class _Arg2>
struct _Project2nd : public binary_function<_Arg1, _Arg2, _Arg2> {
  _Arg2 operator()(const _Arg1&, const _Arg2& __y) const { return __y; }
};

/** The @c operator() of the @c project1st functor takes two arbitrary
 *  arguments and returns the first one, while @c project2nd returns the
 *  second one.  They are extensions provided by SGI.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Arg1, class _Arg2> 
struct project1st : public _Project1st<_Arg1, _Arg2> {};

/// An \link SGIextensions SGI extension \endlink.
template <class _Arg1, class _Arg2>
struct project2nd : public _Project2nd<_Arg1, _Arg2> {};
/** @}  */

// extension documented next
template <class _Result>
struct _Constant_void_fun {
  typedef _Result result_type;
  result_type _M_val;

  _Constant_void_fun(const result_type& __v) : _M_val(__v) {}
  const result_type& operator()() const { return _M_val; }
};  

template <class _Result, class _Argument>
struct _Constant_unary_fun {
  typedef _Argument argument_type;
  typedef  _Result  result_type;
  result_type _M_val;

  _Constant_unary_fun(const result_type& __v) : _M_val(__v) {}
  const result_type& operator()(const _Argument&) const { return _M_val; }
};

template <class _Result, class _Arg1, class _Arg2>
struct _Constant_binary_fun {
  typedef  _Arg1   first_argument_type;
  typedef  _Arg2   second_argument_type;
  typedef  _Result result_type;
  _Result _M_val;

  _Constant_binary_fun(const _Result& __v) : _M_val(__v) {}
  const result_type& operator()(const _Arg1&, const _Arg2&) const {
    return _M_val;
  }
};

/** These three functors are each constructed from a single arbitrary
 *  variable/value.  Later, their @c operator()s completely ignore any
 *  arguments passed, and return the stored value.
 *  - @c constant_void_fun's @c operator() takes no arguments
 *  - @c constant_unary_fun's @c operator() takes one argument (ignored)
 *  - @c constant_binary_fun's @c operator() takes two arguments (ignored)
 *
 *  The helper creator functions @c constant0, @c constant1, and
 *  @c constant2 each take a "result" argument and construct variables of
 *  the appropriate functor type.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
struct constant_void_fun : public _Constant_void_fun<_Result> {
  constant_void_fun(const _Result& __v) : _Constant_void_fun<_Result>(__v) {}
};  

/// An \link SGIextensions SGI extension \endlink.
template <class _Result,
          class _Argument = _Result>
struct constant_unary_fun : public _Constant_unary_fun<_Result, _Argument>
{
  constant_unary_fun(const _Result& __v)
    : _Constant_unary_fun<_Result, _Argument>(__v) {}
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Result,
          class _Arg1 = _Result,
          class _Arg2 = _Arg1>
struct constant_binary_fun
  : public _Constant_binary_fun<_Result, _Arg1, _Arg2>
{
  constant_binary_fun(const _Result& __v)
    : _Constant_binary_fun<_Result, _Arg1, _Arg2>(__v) {}
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_void_fun<_Result> constant0(const _Result& __val)
{
  return constant_void_fun<_Result>(__val);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_unary_fun<_Result,_Result> constant1(const _Result& __val)
{
  return constant_unary_fun<_Result,_Result>(__val);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_binary_fun<_Result,_Result,_Result> 
constant2(const _Result& __val)
{
  return constant_binary_fun<_Result,_Result,_Result>(__val);
}
/** @}  */

/** The @c subtractive_rng class is documented on
 *  <a href="http://www.sgi.com/tech/stl/">SGI's site</a>.
 *  Note that this code assumes that @c int is 32 bits.
 *
 *  @ingroup SGIextensions
*/
class subtractive_rng : public unary_function<unsigned int, unsigned int> {
private:
  unsigned int _M_table[55];
  size_t _M_index1;
  size_t _M_index2;
public:
  /// Returns a number less than the argument.
  unsigned int operator()(unsigned int __limit) {
    _M_index1 = (_M_index1 + 1) % 55;
    _M_index2 = (_M_index2 + 1) % 55;
    _M_table[_M_index1] = _M_table[_M_index1] - _M_table[_M_index2];
    return _M_table[_M_index1] % __limit;
  }

  void _M_initialize(unsigned int __seed)
  {
    unsigned int __k = 1;
    _M_table[54] = __seed;
    size_t __i;
    for (__i = 0; __i < 54; __i++) {
        size_t __ii = (21 * (__i + 1) % 55) - 1;
        _M_table[__ii] = __k;
        __k = __seed - __k;
        __seed = _M_table[__ii];
    }
    for (int __loop = 0; __loop < 4; __loop++) {
        for (__i = 0; __i < 55; __i++)
            _M_table[__i] = _M_table[__i] - _M_table[(1 + __i + 30) % 55];
    }
    _M_index1 = 0;
    _M_index2 = 31;
  }

  /// Ctor allowing you to initialize the seed.
  subtractive_rng(unsigned int __seed) { _M_initialize(__seed); }
  /// Default ctor; initializes its state with some number you don't see.
  subtractive_rng() { _M_initialize(161803398u); }
};


// 20.3.8 adaptors pointers members
/** @defgroup s20_3_8_memadaptors Adaptors for pointers to members
 *  There are a total of 16 = 2^4 function objects in this family.
 *   (1) Member functions taking no arguments vs member functions taking
 *        one argument.
 *   (2) Call through pointer vs call through reference.
 *   (3) Member function with void return type vs member function with
 *       non-void return type.
 *   (4) Const vs non-const member function.
 *
 *  Note that choice (3) is nothing more than a workaround: according
 *   to the draft, compilers should handle void and non-void the same way.
 *   This feature is not yet widely implemented, though.  You can only use
 *   member functions returning void if your compiler supports partial
 *   specialization.
 *
 *  All of this complexity is in the function objects themselves.  You can
 *   ignore it by using the helper function mem_fun and mem_fun_ref,
 *   which create whichever type of adaptor is appropriate.
 *   (mem_fun1 and mem_fun1_ref are no longer part of the C++ standard,
 *   but they are provided for backward compatibility.)
 *
 *  @{
*/
/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp>
class mem_fun_t : public unary_function<_Tp*,_Ret> {
public:
  explicit mem_fun_t(_Ret (_Tp::*__pf)()) : _M_f(__pf) {}
  _Ret operator()(_Tp* __p) const { return (__p->*_M_f)(); }
private:
  _Ret (_Tp::*_M_f)();
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp>
class const_mem_fun_t : public unary_function<const _Tp*,_Ret> {
public:
  explicit const_mem_fun_t(_Ret (_Tp::*__pf)() const) : _M_f(__pf) {}
  _Ret operator()(const _Tp* __p) const { return (__p->*_M_f)(); }
private:
  _Ret (_Tp::*_M_f)() const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp>
class mem_fun_ref_t : public unary_function<_Tp,_Ret> {
public:
  explicit mem_fun_ref_t(_Ret (_Tp::*__pf)()) : _M_f(__pf) {}
  _Ret operator()(_Tp& __r) const { return (__r.*_M_f)(); }
private:
  _Ret (_Tp::*_M_f)();
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp>
class const_mem_fun_ref_t : public unary_function<_Tp,_Ret> {
public:
  explicit const_mem_fun_ref_t(_Ret (_Tp::*__pf)() const) : _M_f(__pf) {}
  _Ret operator()(const _Tp& __r) const { return (__r.*_M_f)(); }
private:
  _Ret (_Tp::*_M_f)() const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp, class _Arg>
class mem_fun1_t : public binary_function<_Tp*,_Arg,_Ret> {
public:
  explicit mem_fun1_t(_Ret (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
  _Ret operator()(_Tp* __p, _Arg __x) const { return (__p->*_M_f)(__x); }
private:
  _Ret (_Tp::*_M_f)(_Arg);
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp, class _Arg>
class const_mem_fun1_t : public binary_function<const _Tp*,_Arg,_Ret> {
public:
  explicit const_mem_fun1_t(_Ret (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
  _Ret operator()(const _Tp* __p, _Arg __x) const
    { return (__p->*_M_f)(__x); }
private:
  _Ret (_Tp::*_M_f)(_Arg) const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp, class _Arg>
class mem_fun1_ref_t : public binary_function<_Tp,_Arg,_Ret> {
public:
  explicit mem_fun1_ref_t(_Ret (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
  _Ret operator()(_Tp& __r, _Arg __x) const { return (__r.*_M_f)(__x); }
private:
  _Ret (_Tp::*_M_f)(_Arg);
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Ret, class _Tp, class _Arg>
class const_mem_fun1_ref_t : public binary_function<_Tp,_Arg,_Ret> {
public:
  explicit const_mem_fun1_ref_t(_Ret (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
  _Ret operator()(const _Tp& __r, _Arg __x) const { return (__r.*_M_f)(__x); }
private:
  _Ret (_Tp::*_M_f)(_Arg) const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp>
class mem_fun_t<void, _Tp> : public unary_function<_Tp*,void> {
public:
  explicit mem_fun_t(void (_Tp::*__pf)()) : _M_f(__pf) {}
  void operator()(_Tp* __p) const { (__p->*_M_f)(); }
private:
  void (_Tp::*_M_f)();
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp>
class const_mem_fun_t<void, _Tp> : public unary_function<const _Tp*,void> {
public:
  explicit const_mem_fun_t(void (_Tp::*__pf)() const) : _M_f(__pf) {}
  void operator()(const _Tp* __p) const { (__p->*_M_f)(); }
private:
  void (_Tp::*_M_f)() const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp>
class mem_fun_ref_t<void, _Tp> : public unary_function<_Tp,void> {
public:
  explicit mem_fun_ref_t(void (_Tp::*__pf)()) : _M_f(__pf) {}
  void operator()(_Tp& __r) const { (__r.*_M_f)(); }
private:
  void (_Tp::*_M_f)();
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp>
class const_mem_fun_ref_t<void, _Tp> : public unary_function<_Tp,void> {
public:
  explicit const_mem_fun_ref_t(void (_Tp::*__pf)() const) : _M_f(__pf) {}
  void operator()(const _Tp& __r) const { (__r.*_M_f)(); }
private:
  void (_Tp::*_M_f)() const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp, class _Arg>
class mem_fun1_t<void, _Tp, _Arg> : public binary_function<_Tp*,_Arg,void> {
public:
  explicit mem_fun1_t(void (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
  void operator()(_Tp* __p, _Arg __x) const { (__p->*_M_f)(__x); }
private:
  void (_Tp::*_M_f)(_Arg);
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp, class _Arg>
class const_mem_fun1_t<void, _Tp, _Arg> 
  : public binary_function<const _Tp*,_Arg,void> {
public:
  explicit const_mem_fun1_t(void (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
  void operator()(const _Tp* __p, _Arg __x) const { (__p->*_M_f)(__x); }
private:
  void (_Tp::*_M_f)(_Arg) const;
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp, class _Arg>
class mem_fun1_ref_t<void, _Tp, _Arg>
  : public binary_function<_Tp,_Arg,void> {
public:
  explicit mem_fun1_ref_t(void (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
  void operator()(_Tp& __r, _Arg __x) const { (__r.*_M_f)(__x); }
private:
  void (_Tp::*_M_f)(_Arg);
};

/// One of the @link s20_3_8_memadaptors adaptors for member pointers@endlink.
template <class _Tp, class _Arg>
class const_mem_fun1_ref_t<void, _Tp, _Arg>
  : public binary_function<_Tp,_Arg,void> {
public:
  explicit const_mem_fun1_ref_t(void (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
  void operator()(const _Tp& __r, _Arg __x) const { (__r.*_M_f)(__x); }
private:
  void (_Tp::*_M_f)(_Arg) const;
};


// Mem_fun adaptor helper functions.  There are only two:
//  mem_fun and mem_fun_ref.  (mem_fun1 and mem_fun1_ref 
//  are provided for backward compatibility, but they are no longer
//  part of the C++ standard.)

template <class _Ret, class _Tp>
inline mem_fun_t<_Ret,_Tp> mem_fun(_Ret (_Tp::*__f)())
  { return mem_fun_t<_Ret,_Tp>(__f); }

template <class _Ret, class _Tp>
inline const_mem_fun_t<_Ret,_Tp> mem_fun(_Ret (_Tp::*__f)() const)
  { return const_mem_fun_t<_Ret,_Tp>(__f); }

template <class _Ret, class _Tp>
inline mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)()) 
  { return mem_fun_ref_t<_Ret,_Tp>(__f); }

template <class _Ret, class _Tp>
inline const_mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)() const)
  { return const_mem_fun_ref_t<_Ret,_Tp>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_t<_Ret,_Tp,_Arg> mem_fun(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_t<_Ret,_Tp,_Arg> mem_fun(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun_ref(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_ref_t<_Ret,_Tp,_Arg>
mem_fun_ref(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun1_ref(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_ref_t<_Ret,_Tp,_Arg>
mem_fun1_ref(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }
/** @}  */

} // namespace std

#endif /* __SGI_STL_INTERNAL_FUNCTION_H */

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