1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Concepts</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../string_algo.html" title="Chapter 2. 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Notation</b></p> 39<div class="table-contents"><table class="table" summary="Notation"> 40<colgroup> 41<col> 42<col> 43</colgroup> 44<tbody> 45<tr> 46<td align="left"><code class="computeroutput">F</code></td> 47<td align="left">A type that is a model of Finder</td> 48</tr> 49<tr> 50<td align="left"><code class="computeroutput">Fmt</code></td> 51<td align="left">A type that is a model of Formatter</td> 52</tr> 53<tr> 54<td align="left"><code class="computeroutput">Iter</code></td> 55<td align="left"> 56 Iterator Type 57 </td> 58</tr> 59<tr> 60<td align="left"><code class="computeroutput">f</code></td> 61<td align="left">Object of type <code class="computeroutput">F</code> 62</td> 63</tr> 64<tr> 65<td align="left"><code class="computeroutput">fmt</code></td> 66<td align="left">Object of type <code class="computeroutput">Fmt</code> 67</td> 68</tr> 69<tr> 70<td align="left"><code class="computeroutput">i,j</code></td> 71<td align="left">Objects of type <code class="computeroutput">Iter</code> 72</td> 73</tr> 74</tbody> 75</table></div> 76</div> 77<br class="table-break"> 78</div> 79<div class="section"> 80<div class="titlepage"><div><div><h3 class="title"> 81<a name="string_algo.finder_concept"></a>Finder Concept</h3></div></div></div> 82<p> 83 Finder is a functor which searches for an arbitrary part of a container. 84 The result of the search is given as an <code class="computeroutput">iterator_range</code> 85 delimiting the selected part. 86 </p> 87<div class="table"> 88<a name="id-1.3.3.8.3.3"></a><p class="title"><b>Table 2.14. Valid Expressions</b></p> 89<div class="table-contents"><table class="table" summary="Valid Expressions"> 90<colgroup> 91<col> 92<col> 93<col> 94</colgroup> 95<thead><tr> 96<th align="left">Expression</th> 97<th align="left">Return Type</th> 98<th align="left">Effects</th> 99</tr></thead> 100<tbody><tr> 101<td align="left"><code class="computeroutput">f(i,j)</code></td> 102<td align="left">Convertible to <code class="computeroutput">iterator_range<Iter></code> 103</td> 104<td align="left">Perform the search on the interval [i,j) and returns the result of the search</td> 105</tr></tbody> 106</table></div> 107</div> 108<br class="table-break"><p> 109 Various algorithms need to perform a search in a container and a Finder is a generalization of such 110 search operations that allows algorithms to abstract from searching. For instance, generic replace 111 algorithms can replace any part of the input, and the Finder is used to select the desired one. 112 </p> 113<p> 114 Note, that it is only required that the finder works with a particular iterator type. However, 115 a Finder operation can be defined as a template, allowing the Finder to work with any iterator. 116 </p> 117<p> 118 <span class="bold"><strong>Examples</strong></span> 119 </p> 120<p> 121 </p> 122<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 123<li class="listitem"> 124 Finder implemented as a class. This Finder always returns the whole input as a match. <code class="computeroutput">operator()</code> 125 is templated, so that the finder can be used on any iterator type. 126 127 <pre class="programlisting"> 128struct simple_finder 129{ 130 template<typename ForwardIteratorT> 131 boost::iterator_range<ForwardIteratorT> operator()( 132 ForwardIteratorT Begin, 133 ForwardIteratorT End ) 134 { 135 return boost::make_range( Begin, End ); 136 } 137}; 138 </pre> 139</li> 140<li class="listitem"> 141 Function Finder. Finder can be any function object. That is, any ordinary function with the 142 required signature can be used as well. However, such a function can be used only for 143 a specific iterator type. 144 145 <pre class="programlisting"> 146boost::iterator_range<std::string> simple_finder( 147 std::string::const_iterator Begin, 148 std::string::const_iterator End ) 149{ 150 return boost::make_range( Begin, End ); 151} 152 </pre> 153</li> 154</ul></div> 155<p> 156 </p> 157</div> 158<div class="section"> 159<div class="titlepage"><div><div><h3 class="title"> 160<a name="string_algo.formatter_concept"></a>Formatter concept</h3></div></div></div> 161<p> 162 Formatters are used by <a class="link" href="design.html#string_algo.replace" title="Replace Algorithms">replace algorithms</a>. 163 They are used in close combination with finders. 164 A formatter is a functor, which takes a result from a Finder operation and transforms it in a specific way. 165 The operation of the formatter can use additional information provided by a specific finder, 166 for example <code class="computeroutput"><a class="link" href="../boost/algorithm/regex_formatter.html" title="Function template regex_formatter">regex_formatter()</a></code> uses the match information from 167 <code class="computeroutput"><a class="link" href="../boost/algorithm/regex_finder.html" title="Function template regex_finder">regex_finder()</a></code> to format the result of formatter operation. 168 </p> 169<div class="table"> 170<a name="id-1.3.3.8.4.3"></a><p class="title"><b>Table 2.15. Valid Expressions</b></p> 171<div class="table-contents"><table class="table" summary="Valid Expressions"> 172<colgroup> 173<col> 174<col> 175<col> 176</colgroup> 177<thead><tr> 178<th align="left">Expression</th> 179<th align="left">Return Type</th> 180<th align="left">Effects</th> 181</tr></thead> 182<tbody><tr> 183<td align="left"><code class="computeroutput">fmt(f(i,j))</code></td> 184<td align="left">A container type, accessible using container traits</td> 185<td align="left">Formats the result of the finder operation</td> 186</tr></tbody> 187</table></div> 188</div> 189<br class="table-break"><p> 190 Similarly to finders, formatters generalize format operations. When a finder is used to 191 select a part of the input, formatter takes this selection and performs some formatting 192 on it. Algorithms can abstract from formatting using a formatter. 193 </p> 194<p> 195 <span class="bold"><strong>Examples</strong></span> 196 </p> 197<p> 198 </p> 199<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 200<li class="listitem"> 201 Formatter implemented as a class. This Formatter does not perform any formatting and 202 returns the match, repackaged. <code class="computeroutput">operator()</code> 203 is templated, so that the Formatter can be used on any Finder type. 204 205 <pre class="programlisting"> 206struct simple_formatter 207{ 208 template<typename FindResultT> 209 std::string operator()( const FindResultT& Match ) 210 { 211 std::string Temp( Match.begin(), Match.end() ); 212 return Temp; 213 } 214}; 215 </pre> 216</li> 217<li class="listitem"> 218 Function Formatter. Similarly to Finder, Formatter can be any function object. 219 However, as a function, it can be used only with a specific Finder type. 220 221 <pre class="programlisting"> 222std::string simple_formatter( boost::iterator_range<std::string::const_iterator>& Match ) 223{ 224 std::string Temp( Match.begin(), Match.end() ); 225 return Temp; 226} 227 </pre> 228</li> 229</ul></div> 230<p> 231 </p> 232</div> 233</div> 234<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 235<td align="left"></td> 236<td align="right"><div class="copyright-footer">Copyright © 2002-2004 Pavol Droba<p>Use, modification and distribution is subject to the Boost 237 Software License, Version 1.0. (See accompanying file 238 <code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 239 </p> 240</div></td> 241</tr></table> 242<hr> 243<div class="spirit-nav"> 244<a accesskey="p" href="design.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../string_algo.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 245</div> 246</body> 247</html> 248
