libstdc++
binders.h
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1 // Functor implementations -*- C++ -*-
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26 /*
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51 
52 /** @file backward/binders.h
53  * This is an internal header file, included by other library headers.
54  * You should not attempt to use it directly.
55  */
56 
57 #ifndef _BACKWARD_BINDERS_H
58 #define _BACKWARD_BINDERS_H 1
59 
60 _GLIBCXX_BEGIN_NAMESPACE(std)
61 
62  // 20.3.6 binders
63  /** @defgroup binders Binder Classes
64  * @ingroup functors
65  *
66  * Binders turn functions/functors with two arguments into functors with
67  * a single argument, storing an argument to be applied later. For
68  * example, a variable @c B of type @c binder1st is constructed from a
69  * functor @c f and an argument @c x. Later, B's @c operator() is called
70  * with a single argument @c y. The return value is the value of @c f(x,y).
71  * @c B can be "called" with various arguments (y1, y2, ...) and will in
72  * turn call @c f(x,y1), @c f(x,y2), ...
73  *
74  * The function @c bind1st is provided to save some typing. It takes the
75  * function and an argument as parameters, and returns an instance of
76  * @c binder1st.
77  *
78  * The type @c binder2nd and its creator function @c bind2nd do the same
79  * thing, but the stored argument is passed as the second parameter instead
80  * of the first, e.g., @c bind2nd(std::minus<float>,1.3) will create a
81  * functor whose @c operator() accepts a floating-point number, subtracts
82  * 1.3 from it, and returns the result. (If @c bind1st had been used,
83  * the functor would perform "1.3 - x" instead.
84  *
85  * Creator-wrapper functions like @c bind1st are intended to be used in
86  * calling algorithms. Their return values will be temporary objects.
87  * (The goal is to not require you to type names like
88  * @c std::binder1st<std::plus<int>> for declaring a variable to hold the
89  * return value from @c bind1st(std::plus<int>,5).
90  *
91  * These become more useful when combined with the composition functions.
92  *
93  * @{
94  */
95  /// One of the @link binders binder functors@endlink.
96  template<typename _Operation>
97  class binder1st
98  : public unary_function<typename _Operation::second_argument_type,
99  typename _Operation::result_type>
100  {
101  protected:
102  _Operation op;
103  typename _Operation::first_argument_type value;
104 
105  public:
106  binder1st(const _Operation& __x,
107  const typename _Operation::first_argument_type& __y)
108  : op(__x), value(__y) { }
109 
110  typename _Operation::result_type
111  operator()(const typename _Operation::second_argument_type& __x) const
112  { return op(value, __x); }
113 
114  // _GLIBCXX_RESOLVE_LIB_DEFECTS
115  // 109. Missing binders for non-const sequence elements
116  typename _Operation::result_type
117  operator()(typename _Operation::second_argument_type& __x) const
118  { return op(value, __x); }
119  } _GLIBCXX_DEPRECATED_ATTR;
120 
121  /// One of the @link binders binder functors@endlink.
122  template<typename _Operation, typename _Tp>
123  inline binder1st<_Operation>
124  bind1st(const _Operation& __fn, const _Tp& __x)
125  {
126  typedef typename _Operation::first_argument_type _Arg1_type;
127  return binder1st<_Operation>(__fn, _Arg1_type(__x));
128  }
129 
130  /// One of the @link binders binder functors@endlink.
131  template<typename _Operation>
132  class binder2nd
133  : public unary_function<typename _Operation::first_argument_type,
134  typename _Operation::result_type>
135  {
136  protected:
137  _Operation op;
138  typename _Operation::second_argument_type value;
139 
140  public:
141  binder2nd(const _Operation& __x,
142  const typename _Operation::second_argument_type& __y)
143  : op(__x), value(__y) { }
144 
145  typename _Operation::result_type
146  operator()(const typename _Operation::first_argument_type& __x) const
147  { return op(__x, value); }
148 
149  // _GLIBCXX_RESOLVE_LIB_DEFECTS
150  // 109. Missing binders for non-const sequence elements
151  typename _Operation::result_type
152  operator()(typename _Operation::first_argument_type& __x) const
153  { return op(__x, value); }
154  } _GLIBCXX_DEPRECATED_ATTR;
155 
156  /// One of the @link binders binder functors@endlink.
157  template<typename _Operation, typename _Tp>
158  inline binder2nd<_Operation>
159  bind2nd(const _Operation& __fn, const _Tp& __x)
160  {
161  typedef typename _Operation::second_argument_type _Arg2_type;
162  return binder2nd<_Operation>(__fn, _Arg2_type(__x));
163  }
164  /** @} */
165 
166 _GLIBCXX_END_NAMESPACE
167 
168 #endif /* _BACKWARD_BINDERS_H */
binder2nd< _Operation > bind2nd(const _Operation &__fn, const _Tp &__x)
One of the binder functors.
Definition: binders.h:159
binder1st< _Operation > bind1st(const _Operation &__fn, const _Tp &__x)
One of the binder functors.
Definition: binders.h:124
_Operation::result_type result_type
result_type is the return type
Definition: stl_function.h:105
One of the binder functors.
Definition: binders.h:97
One of the binder functors.
Definition: binders.h:132