libstdc++

binders.h
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1 // Functor implementations -*- C++ -*-
2
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25 /*
26 *
27 * Copyright (c) 1994
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39 * Copyright (c) 1996-1998
40 * Silicon Graphics Computer Systems, Inc.
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42 * Permission to use, copy, modify, distribute and sell this software
43 * and its documentation for any purpose is hereby granted without fee,
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49 */
50
51 /** @file backward/binders.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{functional}
54 */
55
56 #ifndef _BACKWARD_BINDERS_H
57 #define _BACKWARD_BINDERS_H 1
58
59 namespace std _GLIBCXX_VISIBILITY(default)
60 {
61 _GLIBCXX_BEGIN_NAMESPACE_VERSION
62
63 // 20.3.6 binders
64 /** @defgroup binders Binder Classes
65 * @ingroup functors
66 *
67 * Binders turn functions/functors with two arguments into functors
68 * with a single argument, storing an argument to be applied later.
69 * For example, a variable @c B of type @c binder1st is constructed
70 * from a functor @c f and an argument @c x. Later, B's @c
71 * operator() is called with a single argument @c y. The return
72 * value is the value of @c f(x,y). @c B can be @a called with
73 * various arguments (y1, y2, ...) and will in turn call @c
74 * f(x,y1), @c f(x,y2), ...
75 *
76 * The function @c bind1st is provided to save some typing. It takes the
77 * function and an argument as parameters, and returns an instance of
78 * @c binder1st.
79 *
80 * The type @c binder2nd and its creator function @c bind2nd do the same
81 * thing, but the stored argument is passed as the second parameter instead
82 * of the first, e.g., @c bind2nd(std::minus<float>(),1.3) will create a
83 * functor whose @c operator() accepts a floating-point number, subtracts
84 * 1.3 from it, and returns the result. (If @c bind1st had been used,
85 * the functor would perform <em>1.3 - x</em> instead.
86 *
87 * Creator-wrapper functions like @c bind1st are intended to be used in
88 * calling algorithms. Their return values will be temporary objects.
89 * (The goal is to not require you to type names like
90 * @c std::binder1st<std::plus<int>> for declaring a variable to hold the
91 * return value from @c bind1st(std::plus<int>(),5).
92 *
93 * These become more useful when combined with the composition functions.
94 *
95 * These functions are deprecated in C++11 and can be replaced by
96 * @c std::bind (or @c std::tr1::bind) which is more powerful and flexible,
97 * supporting functions with any number of arguments. Uses of @c bind1st
98 * can be replaced by @c std::bind(f, x, std::placeholders::_1) and
99 * @c bind2nd by @c std::bind(f, std::placeholders::_1, x).
100 * @{
101 */
102 /// One of the @link binders binder functors@endlink.
103 template<typename _Operation>
104 class binder1st
105 : public unary_function<typename _Operation::second_argument_type,
106 typename _Operation::result_type>
107 {
108 protected:
109 _Operation op;
110 typename _Operation::first_argument_type value;
111
112 public:
113 binder1st(const _Operation& __x,
114 const typename _Operation::first_argument_type& __y)
115 : op(__x), value(__y) { }
116
117 typename _Operation::result_type
118 operator()(const typename _Operation::second_argument_type& __x) const
119 { return op(value, __x); }
120
121 // _GLIBCXX_RESOLVE_LIB_DEFECTS
122 // 109. Missing binders for non-const sequence elements
123 typename _Operation::result_type
124 operator()(typename _Operation::second_argument_type& __x) const
125 { return op(value, __x); }
126 } _GLIBCXX_DEPRECATED;
127
128 /// One of the @link binders binder functors@endlink.
129 template<typename _Operation, typename _Tp>
130 inline binder1st<_Operation>
131 bind1st(const _Operation& __fn, const _Tp& __x)
132 {
133 typedef typename _Operation::first_argument_type _Arg1_type;
134 return binder1st<_Operation>(__fn, _Arg1_type(__x));
135 }
136
137 /// One of the @link binders binder functors@endlink.
138 template<typename _Operation>
139 class binder2nd
140 : public unary_function<typename _Operation::first_argument_type,
141 typename _Operation::result_type>
142 {
143 protected:
144 _Operation op;
145 typename _Operation::second_argument_type value;
146
147 public:
148 binder2nd(const _Operation& __x,
149 const typename _Operation::second_argument_type& __y)
150 : op(__x), value(__y) { }
151
152 typename _Operation::result_type
153 operator()(const typename _Operation::first_argument_type& __x) const
154 { return op(__x, value); }
155
156 // _GLIBCXX_RESOLVE_LIB_DEFECTS
157 // 109. Missing binders for non-const sequence elements
158 typename _Operation::result_type
159 operator()(typename _Operation::first_argument_type& __x) const
160 { return op(__x, value); }
161 } _GLIBCXX_DEPRECATED;
162
163 /// One of the @link binders binder functors@endlink.
164 template<typename _Operation, typename _Tp>
165 inline binder2nd<_Operation>
166 bind2nd(const _Operation& __fn, const _Tp& __x)
167 {
168 typedef typename _Operation::second_argument_type _Arg2_type;
169 return binder2nd<_Operation>(__fn, _Arg2_type(__x));
170 }
171 /** @} */
172
173 _GLIBCXX_END_NAMESPACE_VERSION
174 } // namespace
175
176 #endif /* _BACKWARD_BINDERS_H */