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4<head>
5  <meta http-equiv="Content-Language" content="en-us">
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8  <title>Generator Iterator Adaptor Documentation</title>
9</head>
10
11<body bgcolor="#FFFFFF" text="#000000">
12  <img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle"
13  width="277" height="86">
14
15  <h1>Generator Iterator Adaptor</h1>
16
17  <p>Defined in header <a href=
18  "../../boost/generator_iterator.hpp">boost/generator_iterator.hpp</a></p>
19
20  <p>The generator iterator adaptor makes it easier to create custom input
21  iterators from 0-ary functions and function objects. The adaptor takes a
22  <a href="http://www.sgi.com/tech/stl/Generator.html">Generator</a> and
23  creates a model of <a href=
24  "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>. Each
25  increment retrieves an item from the generator and makes it available to be
26  retrieved by dereferencing. The motivation for this iterator is that some
27  concepts can be more naturally expressed as a generator, while most STL
28  algorithms expect an iterator. An example is the <a href=
29  "../random/index.html">Random Number</a> library.</p>
30
31  <h2>Synopsis</h2>
32
33  <blockquote>
34    <pre>
35namespace boost {
36  template &lt;class Generator&gt;
37  class generator_iterator_policies;
38
39  template &lt;class Generator&gt;
40  class generator_iterator_generator;
41
42  template &lt;class Generator&gt;
43  typename generator_iterator_generator&lt;Generator&gt;::type
44  make_generator_iterator(Generator &amp; gen);
45}
46</pre>
47  </blockquote>
48  <hr>
49
50  <h2>The Generator Iterator Generator Class</h2>
51
52  <p>The class generator_iterator_generator is a helper class whose purpose
53  is to construct a generator iterator type. The template parameter for this
54  class is the Generator function object type that is being wrapped. The
55  generator iterator adaptor only holds a reference (or pointer) to the
56  function object, therefore the function object must outlive the generator
57  iterator adaptor constructed from it.</p>
58  <pre>
59template &lt;class Generator&gt;
60class generator_iterator_generator
61{
62public:
63  typedef <i>unspecified</i> type; // the resulting generator iterator type
64}
65</pre>
66
67  <h3>Template Parameters</h3>
68
69  <table border summary="">
70    <tr>
71      <th>Parameter</th>
72
73      <th>Description</th>
74    </tr>
75
76    <tr>
77      <td><tt><a href=
78      "http://www.sgi.com/tech/stl/Generator.html">Generator</a></tt></td>
79
80      <td>The generator (0-ary function object) type being wrapped. The
81      return type of the function must be defined as
82      <tt>Generator::result_type</tt>. The function object must be a model of
83      <a href=
84      "http://www.sgi.com/tech/stl/Generator.html">Generator</a>.</td>
85    </tr>
86  </table>
87
88  <h3>Concept Model</h3>
89
90  <p>The generator iterator class is a model of <a href=
91  "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>.</p>
92
93  <h3>Members</h3>
94
95  <p>The generator iterator implements the member functions and operators
96  required of the <a href=
97  "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>
98  concept.<br></p>
99  <hr>
100
101  <h2><a name="make_generator_iterator" id="make_generator_iterator">The
102  Generator Iterator Object Generator</a></h2>
103
104  <p>The <tt>make_generator_iterator()</tt> function provides a convenient
105  way to create generator iterator objects. The function saves the user the
106  trouble of explicitly writing out the iterator types.</p>
107
108  <blockquote>
109    <pre>
110template &lt;class Generator&gt;
111typename generator_iterator_generator&lt;Generator&gt;::type
112make_generator_iterator(Generator &amp; gen);
113</pre>
114  </blockquote>
115  <hr>
116
117  <h3>Example</h3>
118
119  <p>The following program shows how <code>generator_iterator</code>
120  transforms a generator into an input iterator.</p>
121
122  <blockquote>
123    <pre>
124#include &lt;iostream&gt;
125#include &lt;boost/generator_iterator.hpp&gt;
126
127class my_generator
128{
129public:
130  typedef int result_type;
131  my_generator() : state(0) { }
132  int operator()() { return ++state; }
133private:
134  int state;
135};
136
137int main()
138{
139  my_generator gen;
140  boost::generator_iterator_generator&lt;my_generator&gt;::type it = boost::make_generator_iterator(gen);
141  for(int i = 0; i &lt; 10; ++i, ++it)
142    std::cout &lt;&lt; *it &lt;&lt; std::endl;
143}
144</pre>
145  </blockquote>
146  <hr>
147
148  <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
149  "http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
150  height="31" width="88"></a></p>
151
152  <p>Revised
153  <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
154
155  <p><i>Copyright &copy; 2001 <a href=
156  "../../people/jens_maurer.htm">Jens Maurer</a></i></p>
157
158  <p><i>Distributed under the Boost Software License, Version 1.0. (See
159  accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
160  copy at <a href=
161  "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
162</body>
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