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2 | Copyright 2007 John Maddock. | |
3 | Distributed under the Boost Software License, Version 1.0. | |
4 | (See accompanying file LICENSE_1_0.txt or copy at | |
5 | http://www.boost.org/LICENSE_1_0.txt). | |
6 | ] | |
7 | ||
8 | [section:examples Examples] | |
9 | ||
10 | [section:copy An Optimized Version of std::copy] | |
11 | ||
12 | Demonstrates a version of `std::copy` that uses `__has_trivial_assign` to | |
13 | determine whether to use `memcpy` to optimise the copy operation | |
14 | (see [@../../examples/copy_example.cpp copy_example.cpp]): | |
15 | ||
16 | // | |
17 | // opt::copy | |
18 | // same semantics as std::copy | |
19 | // calls memcpy where appropriate. | |
20 | // | |
21 | ||
22 | namespace detail{ | |
23 | ||
24 | template<typename I1, typename I2, bool b> | |
25 | I2 copy_imp(I1 first, I1 last, I2 out, const boost::__integral_constant<bool, b>&) | |
26 | { | |
27 | while(first != last) | |
28 | { | |
29 | *out = *first; | |
30 | ++out; | |
31 | ++first; | |
32 | } | |
33 | return out; | |
34 | } | |
35 | ||
36 | template<typename T> | |
37 | T* copy_imp(const T* first, const T* last, T* out, const boost::__true_type&) | |
38 | { | |
39 | memmove(out, first, (last-first)*sizeof(T)); | |
40 | return out+(last-first); | |
41 | } | |
42 | ||
43 | ||
44 | } | |
45 | ||
46 | template<typename I1, typename I2> | |
47 | inline I2 copy(I1 first, I1 last, I2 out) | |
48 | { | |
49 | // | |
50 | // We can copy with memcpy if T has a trivial assignment operator, | |
51 | // and if the iterator arguments are actually pointers (this last | |
52 | // requirement we detect with overload resolution): | |
53 | // | |
54 | typedef typename std::iterator_traits<I1>::value_type value_type; | |
55 | return detail::copy_imp(first, last, out, boost::__has_trivial_assign<value_type>()); | |
56 | } | |
57 | ||
58 | ||
59 | [endsect] | |
60 | ||
61 | [section:fill An Optimised Version of std::fill] | |
62 | ||
63 | Demonstrates a version of `std::fill` that uses `__has_trivial_assign` to | |
64 | determine whether to use `memset` to optimise the fill operation | |
65 | (see [@../../examples/fill_example.cpp fill_example.cpp]): | |
66 | ||
67 | // | |
68 | // fill | |
69 | // same as std::fill, but uses memset where appropriate | |
70 | // | |
71 | namespace detail{ | |
72 | ||
73 | template <typename I, typename T, bool b> | |
74 | void do_fill(I first, I last, const T& val, const boost::__integral_constant<bool, b>&) | |
75 | { | |
76 | while(first != last) | |
77 | { | |
78 | *first = val; | |
79 | ++first; | |
80 | } | |
81 | } | |
82 | ||
83 | template <typename T> | |
84 | void do_fill(T* first, T* last, const T& val, const boost::__true_type&) | |
85 | { | |
86 | std::memset(first, val, last-first); | |
87 | } | |
88 | ||
89 | } | |
90 | ||
91 | template <class I, class T> | |
92 | inline void fill(I first, I last, const T& val) | |
93 | { | |
94 | // | |
95 | // We can do an optimised fill if T has a trivial assignment | |
96 | // operator and if it's size is one: | |
97 | // | |
98 | typedef boost::__integral_constant<bool, | |
99 | ::boost::__has_trivial_assign<T>::value && (sizeof(T) == 1)> truth_type; | |
100 | detail::do_fill(first, last, val, truth_type()); | |
101 | } | |
102 | ||
103 | ||
104 | [endsect] | |
105 | ||
106 | [section:destruct An Example that Omits Destructor Calls For Types with Trivial Destructors] | |
107 | ||
108 | Demonstrates a simple algorithm that uses `__has_trivial_destruct` to | |
109 | determine whether to destructors need to be called | |
110 | (see [@../../examples/trivial_destructor_example.cpp trivial_destructor_example.cpp]): | |
111 | ||
112 | // | |
113 | // algorithm destroy_array: | |
114 | // The reverse of std::unitialized_copy, takes a block of | |
115 | // initialized memory and calls destructors on all objects therein. | |
116 | // | |
117 | ||
118 | namespace detail{ | |
119 | ||
120 | template <class T> | |
121 | void do_destroy_array(T* first, T* last, const boost::__false_type&) | |
122 | { | |
123 | while(first != last) | |
124 | { | |
125 | first->~T(); | |
126 | ++first; | |
127 | } | |
128 | } | |
129 | ||
130 | template <class T> | |
131 | inline void do_destroy_array(T* first, T* last, const boost::__true_type&) | |
132 | { | |
133 | } | |
134 | ||
135 | } // namespace detail | |
136 | ||
137 | template <class T> | |
138 | inline void destroy_array(T* p1, T* p2) | |
139 | { | |
140 | detail::do_destroy_array(p1, p2, ::boost::__has_trivial_destructor<T>()); | |
141 | } | |
142 | ||
143 | ||
144 | [endsect] | |
145 | ||
146 | [section:iter An improved Version of std::iter_swap] | |
147 | ||
148 | Demonstrates a version of `std::iter_swap` that use type traits to | |
149 | determine whether an it's arguments are proxy iterators or not, | |
150 | if they're not then it just does a `std::swap` of it's dereferenced | |
151 | arguments (the | |
152 | same as `std::iter_swap` does), however if they are proxy iterators | |
153 | then takes special care over the swap to ensure that the algorithm | |
154 | works correctly for both proxy iterators, and even iterators of | |
155 | different types | |
156 | (see [@../../examples/iter_swap_example.cpp iter_swap_example.cpp]): | |
157 | ||
158 | // | |
159 | // iter_swap: | |
160 | // tests whether iterator is a proxy iterator or not, and | |
161 | // uses optimal form accordingly: | |
162 | // | |
163 | namespace detail{ | |
164 | ||
165 | template <typename I> | |
166 | static void do_swap(I one, I two, const boost::__false_type&) | |
167 | { | |
168 | typedef typename std::iterator_traits<I>::value_type v_t; | |
169 | v_t v = *one; | |
170 | *one = *two; | |
171 | *two = v; | |
172 | } | |
173 | template <typename I> | |
174 | static void do_swap(I one, I two, const boost::__true_type&) | |
175 | { | |
176 | using std::swap; | |
177 | swap(*one, *two); | |
178 | } | |
179 | ||
180 | } | |
181 | ||
182 | template <typename I1, typename I2> | |
183 | inline void iter_swap(I1 one, I2 two) | |
184 | { | |
185 | // | |
186 | // See is both arguments are non-proxying iterators, | |
187 | // and if both iterator the same type: | |
188 | // | |
189 | typedef typename std::iterator_traits<I1>::reference r1_t; | |
190 | typedef typename std::iterator_traits<I2>::reference r2_t; | |
191 | ||
192 | typedef boost::__integral_constant<bool, | |
193 | ::boost::__is_reference<r1_t>::value | |
194 | && ::boost::__is_reference<r2_t>::value | |
195 | && ::boost::__is_same<r1_t, r2_t>::value> truth_type; | |
196 | ||
197 | detail::do_swap(one, two, truth_type()); | |
198 | } | |
199 | ||
200 | ||
201 | [endsect] | |
202 | ||
203 | [section:to_double Convert Numeric Types and Enums to double] | |
204 | ||
205 | Demonstrates a conversion of | |
206 | [@../../../../libs/numeric/conversion/doc/html/boost_numericconversion/definitions.html#boost_numericconversion.definitions.numeric_types | |
207 | Numeric Types] | |
208 | and enum types to double: | |
209 | ||
210 | template<class T> | |
211 | inline double to_double(T const& value) | |
212 | { | |
213 | typedef typename boost::promote<T>::type promoted; | |
214 | return boost::numeric::converter<double,promoted>::convert(value); | |
215 | } | |
216 | ||
217 | [endsect] | |
218 | ||
219 | [section:improved_min Improving std::min with common_type] | |
220 | ||
221 | An improved `std::min` function could be written like this: | |
222 | ||
223 | template <class T, class U> | |
224 | typename __common_type<T, U>::type min(T t, U u) | |
225 | { | |
226 | return t < u ? t : u; | |
227 | } | |
228 | ||
229 | And now expressions such as: | |
230 | ||
231 | min(1, 2.0) | |
232 | ||
233 | will actually compile and return the correct type! | |
234 | ||
235 | [endsect] | |
236 | [endsect] | |
237 |