stl_function.h

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

// Copyright (C) 2001, 2002, 2004 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
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// invalidate any other reasons why the executable file might be covered by
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/*
 *
 * 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 _FUNCTION_H
#define _FUNCTION_H 1

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; }
    };
    /** @}  */

    // 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