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<title>Generator Iterator Adaptor Documentation</title>
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<img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle"
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<h1>Generator Iterator Adaptor</h1>
<p>Defined in header <a href=
"../../boost/generator_iterator.hpp">boost/generator_iterator.hpp</a></p>
<p>The generator iterator adaptor makes it easier to create custom input
iterators from 0-ary functions and function objects. The adaptor takes a
<a href="http://www.sgi.com/tech/stl/Generator.html">Generator</a> and
creates a model of <a href=
"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>. Each
increment retrieves an item from the generator and makes it available to be
retrieved by dereferencing. The motivation for this iterator is that some
concepts can be more naturally expressed as a generator, while most STL
algorithms expect an iterator. An example is the <a href=
"../random/index.html">Random Number</a> library.</p>
<h2>Synopsis</h2>
<blockquote>
<pre>
namespace boost {
template <class Generator>
class generator_iterator_policies;
template <class Generator>
class generator_iterator_generator;
template <class Generator>
typename generator_iterator_generator<Generator>::type
make_generator_iterator(Generator & gen);
}
</pre>
</blockquote>
<hr>
<h2>The Generator Iterator Generator Class</h2>
<p>The class generator_iterator_generator is a helper class whose purpose
is to construct a generator iterator type. The template parameter for this
class is the Generator function object type that is being wrapped. The
generator iterator adaptor only holds a reference (or pointer) to the
function object, therefore the function object must outlive the generator
iterator adaptor constructed from it.</p>
<pre>
template <class Generator>
class generator_iterator_generator
{
public:
typedef <i>unspecified</i> type; // the resulting generator iterator type
}
</pre>
<h3>Template Parameters</h3>
<table border summary="">
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr>
<td><tt><a href=
"http://www.sgi.com/tech/stl/Generator.html">Generator</a></tt></td>
<td>The generator (0-ary function object) type being wrapped. The
return type of the function must be defined as
<tt>Generator::result_type</tt>. The function object must be a model of
<a href=
"http://www.sgi.com/tech/stl/Generator.html">Generator</a>.</td>
</tr>
</table>
<h3>Concept Model</h3>
<p>The generator iterator class is a model of <a href=
"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>.</p>
<h3>Members</h3>
<p>The generator iterator implements the member functions and operators
required of the <a href=
"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>
concept.<br></p>
<hr>
<h2><a name="make_generator_iterator" id="make_generator_iterator">The
Generator Iterator Object Generator</a></h2>
<p>The <tt>make_generator_iterator()</tt> function provides a convenient
way to create generator iterator objects. The function saves the user the
trouble of explicitly writing out the iterator types.</p>
<blockquote>
<pre>
template <class Generator>
typename generator_iterator_generator<Generator>::type
make_generator_iterator(Generator & gen);
</pre>
</blockquote>
<hr>
<h3>Example</h3>
<p>The following program shows how <code>generator_iterator</code>
transforms a generator into an input iterator.</p>
<blockquote>
<pre>
#include <iostream>
#include <boost/generator_iterator.hpp>
class my_generator
{
public:
typedef int result_type;
my_generator() : state(0) { }
int operator()() { return ++state; }
private:
int state;
};
int main()
{
my_generator gen;
boost::generator_iterator_generator<my_generator>::type it = boost::make_generator_iterator(gen);
for(int i = 0; i < 10; ++i, ++it)
std::cout << *it << std::endl;
}
</pre>
</blockquote>
<hr>
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<p>Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
<p><i>Copyright © 2001 <a href=
"../../people/jens_maurer.htm">Jens Maurer</a></i></p>
<p><i>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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