1 // Functor implementations -*- C++ -*-
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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}
57 #ifndef _BACKWARD_BINDERS_H
58 #define _BACKWARD_BINDERS_H 1
60 namespace std _GLIBCXX_VISIBILITY(default)
62 _GLIBCXX_BEGIN_NAMESPACE_VERSION
65 /** @defgroup binders Binder Classes
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), ...
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
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.
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).
94 * These become more useful when combined with the composition functions.
98 /// One of the @link binders binder functors@endlink.
99 template<typename _Operation>
101 : public unary_function<typename _Operation::second_argument_type,
102 typename _Operation::result_type>
106 typename _Operation::first_argument_type value;
109 binder1st(const _Operation& __x,
110 const typename _Operation::first_argument_type& __y)
111 : op(__x), value(__y) { }
113 typename _Operation::result_type
114 operator()(const typename _Operation::second_argument_type& __x) const
115 { return op(value, __x); }
117 // _GLIBCXX_RESOLVE_LIB_DEFECTS
118 // 109. Missing binders for non-const sequence elements
119 typename _Operation::result_type
120 operator()(typename _Operation::second_argument_type& __x) const
121 { return op(value, __x); }
122 } _GLIBCXX_DEPRECATED;
124 /// One of the @link binders binder functors@endlink.
125 template<typename _Operation, typename _Tp>
126 inline binder1st<_Operation>
127 bind1st(const _Operation& __fn, const _Tp& __x)
129 typedef typename _Operation::first_argument_type _Arg1_type;
130 return binder1st<_Operation>(__fn, _Arg1_type(__x));
133 /// One of the @link binders binder functors@endlink.
134 template<typename _Operation>
136 : public unary_function<typename _Operation::first_argument_type,
137 typename _Operation::result_type>
141 typename _Operation::second_argument_type value;
144 binder2nd(const _Operation& __x,
145 const typename _Operation::second_argument_type& __y)
146 : op(__x), value(__y) { }
148 typename _Operation::result_type
149 operator()(const typename _Operation::first_argument_type& __x) const
150 { return op(__x, value); }
152 // _GLIBCXX_RESOLVE_LIB_DEFECTS
153 // 109. Missing binders for non-const sequence elements
154 typename _Operation::result_type
155 operator()(typename _Operation::first_argument_type& __x) const
156 { return op(__x, value); }
157 } _GLIBCXX_DEPRECATED;
159 /// One of the @link binders binder functors@endlink.
160 template<typename _Operation, typename _Tp>
161 inline binder2nd<_Operation>
162 bind2nd(const _Operation& __fn, const _Tp& __x)
164 typedef typename _Operation::second_argument_type _Arg2_type;
165 return binder2nd<_Operation>(__fn, _Arg2_type(__x));
169 _GLIBCXX_END_NAMESPACE_VERSION
172 #endif /* _BACKWARD_BINDERS_H */