binders.h

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

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 *
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 * Hewlett-Packard Company
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/** @file backward/binders.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{functional}
 */

#ifndef _BACKWARD_BINDERS_H
#define _BACKWARD_BINDERS_H 1

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // 20.3.6 binders
  /** @defgroup binders Binder Classes
   * @ingroup functors
   *
   *  Binders turn functions/functors with two arguments into functors
   *  with a single argument, storing an argument to be applied later.
   *  For example, a 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 @a 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 <em>1.3 - x</em> 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.
   *
   *  These functions are deprecated in C++11 and can be replaced by
   *  @c std::bind (or @c std::tr1::bind) which is more powerful and flexible,
   *  supporting functions with any number of arguments.  Uses of @c bind1st
   *  can be replaced by @c std::bind(f, x, std::placeholders::_1) and
   *  @c bind2nd by @c std::bind(f, std::placeholders::_1, x).
   *  @{
   */
  /// One of the @link binders binder functors@endlink.
  template<typename _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); }

      // _GLIBCXX_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); }
    } _GLIBCXX_DEPRECATED;

  /// One of the @link binders binder functors@endlink.
  template<typename _Operation, typename _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 binders binder functors@endlink.
  template<typename _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); }

      // _GLIBCXX_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); }
    } _GLIBCXX_DEPRECATED;

  /// One of the @link binders binder functors@endlink.
  template<typename _Operation, typename _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));
    } 
  /** @}  */

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _BACKWARD_BINDERS_H */