libstdc++
binders.h
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51 
52 /** @file backward/binders.h
53  * This is an internal header file, included by other library headers.
54  * Do not attempt to use it directly. @headername{functional}
55  */
56 
57 #ifndef _BACKWARD_BINDERS_H
58 #define _BACKWARD_BINDERS_H 1
59 
60 namespace std _GLIBCXX_VISIBILITY(default)
61 {
62 _GLIBCXX_BEGIN_NAMESPACE_VERSION
63 
64  // 20.3.6 binders
65  /** @defgroup binders Binder Classes
66  * @ingroup functors
67  *
68  * Binders turn functions/functors with two arguments into functors
69  * with a single argument, storing an argument to be applied later.
70  * For example, a variable @c B of type @c binder1st is constructed
71  * from a functor @c f and an argument @c x. Later, B's @c
72  * operator() is called with a single argument @c y. The return
73  * value is the value of @c f(x,y). @c B can be @a called with
74  * various arguments (y1, y2, ...) and will in turn call @c
75  * f(x,y1), @c f(x,y2), ...
76  *
77  * The function @c bind1st is provided to save some typing. It takes the
78  * function and an argument as parameters, and returns an instance of
79  * @c binder1st.
80  *
81  * The type @c binder2nd and its creator function @c bind2nd do the same
82  * thing, but the stored argument is passed as the second parameter instead
83  * of the first, e.g., @c bind2nd(std::minus<float>(),1.3) will create a
84  * functor whose @c operator() accepts a floating-point number, subtracts
85  * 1.3 from it, and returns the result. (If @c bind1st had been used,
86  * the functor would perform <em>1.3 - x</em> instead.
87  *
88  * Creator-wrapper functions like @c bind1st are intended to be used in
89  * calling algorithms. Their return values will be temporary objects.
90  * (The goal is to not require you to type names like
91  * @c std::binder1st<std::plus<int>> for declaring a variable to hold the
92  * return value from @c bind1st(std::plus<int>(),5).
93  *
94  * These become more useful when combined with the composition functions.
95  *
96  * These functions are deprecated in C++11 and can be replaced by
97  * @c std::bind (or @c std::tr1::bind) which is more powerful and flexible,
98  * supporting functions with any number of arguments. Uses of @c bind1st
99  * can be replaced by @c std::bind(f, x, std::placeholders::_1) and
100  * @c bind2nd by @c std::bind(f, std::placeholders::_1, x).
101  * @{
102  */
103  /// One of the @link binders binder functors@endlink.
104  template<typename _Operation>
105  class binder1st
106  : public unary_function<typename _Operation::second_argument_type,
107  typename _Operation::result_type>
108  {
109  protected:
110  _Operation op;
111  typename _Operation::first_argument_type value;
112 
113  public:
114  binder1st(const _Operation& __x,
115  const typename _Operation::first_argument_type& __y)
116  : op(__x), value(__y) { }
117 
118  typename _Operation::result_type
119  operator()(const typename _Operation::second_argument_type& __x) const
120  { return op(value, __x); }
121 
122  // _GLIBCXX_RESOLVE_LIB_DEFECTS
123  // 109. Missing binders for non-const sequence elements
124  typename _Operation::result_type
125  operator()(typename _Operation::second_argument_type& __x) const
126  { return op(value, __x); }
127  } _GLIBCXX_DEPRECATED;
128 
129  /// One of the @link binders binder functors@endlink.
130  template<typename _Operation, typename _Tp>
131  inline binder1st<_Operation>
132  bind1st(const _Operation& __fn, const _Tp& __x)
133  {
134  typedef typename _Operation::first_argument_type _Arg1_type;
135  return binder1st<_Operation>(__fn, _Arg1_type(__x));
136  }
137 
138  /// One of the @link binders binder functors@endlink.
139  template<typename _Operation>
140  class binder2nd
141  : public unary_function<typename _Operation::first_argument_type,
142  typename _Operation::result_type>
143  {
144  protected:
145  _Operation op;
146  typename _Operation::second_argument_type value;
147 
148  public:
149  binder2nd(const _Operation& __x,
150  const typename _Operation::second_argument_type& __y)
151  : op(__x), value(__y) { }
152 
153  typename _Operation::result_type
154  operator()(const typename _Operation::first_argument_type& __x) const
155  { return op(__x, value); }
156 
157  // _GLIBCXX_RESOLVE_LIB_DEFECTS
158  // 109. Missing binders for non-const sequence elements
159  typename _Operation::result_type
160  operator()(typename _Operation::first_argument_type& __x) const
161  { return op(__x, value); }
162  } _GLIBCXX_DEPRECATED;
163 
164  /// One of the @link binders binder functors@endlink.
165  template<typename _Operation, typename _Tp>
166  inline binder2nd<_Operation>
167  bind2nd(const _Operation& __fn, const _Tp& __x)
168  {
169  typedef typename _Operation::second_argument_type _Arg2_type;
170  return binder2nd<_Operation>(__fn, _Arg2_type(__x));
171  }
172  /** @} */
173 
174 _GLIBCXX_END_NAMESPACE_VERSION
175 } // namespace
176 
177 #endif /* _BACKWARD_BINDERS_H */