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164 lines
5.0 KiB
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<meta http-equiv="Content-Language" content="en-us">
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<title>Generator Iterator Adaptor Documentation</title>
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<body bgcolor="#FFFFFF" text="#000000">
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<img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle"
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width="277" height="86">
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<h1>Generator Iterator Adaptor</h1>
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<p>Defined in header <a href=
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"../../boost/generator_iterator.hpp">boost/generator_iterator.hpp</a></p>
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<p>The generator iterator adaptor makes it easier to create custom input
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iterators from 0-ary functions and function objects. The adaptor takes a
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<a href="http://www.sgi.com/tech/stl/Generator.html">Generator</a> and
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creates a model of <a href=
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"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>. Each
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increment retrieves an item from the generator and makes it available to be
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retrieved by dereferencing. The motivation for this iterator is that some
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concepts can be more naturally expressed as a generator, while most STL
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algorithms expect an iterator. An example is the <a href=
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"../random/index.html">Random Number</a> library.</p>
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<h2>Synopsis</h2>
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<blockquote>
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<pre>
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namespace boost {
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template <class Generator>
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class generator_iterator_policies;
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template <class Generator>
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class generator_iterator_generator;
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template <class Generator>
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typename generator_iterator_generator<Generator>::type
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make_generator_iterator(Generator & gen);
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}
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</pre>
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</blockquote>
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<hr>
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<h2>The Generator Iterator Generator Class</h2>
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<p>The class generator_iterator_generator is a helper class whose purpose
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is to construct a generator iterator type. The template parameter for this
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class is the Generator function object type that is being wrapped. The
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generator iterator adaptor only holds a reference (or pointer) to the
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function object, therefore the function object must outlive the generator
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iterator adaptor constructed from it.</p>
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<pre>
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template <class Generator>
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class generator_iterator_generator
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{
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public:
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typedef <i>unspecified</i> type; // the resulting generator iterator type
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}
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</pre>
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<h3>Template Parameters</h3>
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<table border summary="">
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<tr>
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<th>Parameter</th>
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<th>Description</th>
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</tr>
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<tr>
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<td><tt><a href=
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"http://www.sgi.com/tech/stl/Generator.html">Generator</a></tt></td>
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<td>The generator (0-ary function object) type being wrapped. The
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return type of the function must be defined as
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<tt>Generator::result_type</tt>. The function object must be a model of
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<a href=
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"http://www.sgi.com/tech/stl/Generator.html">Generator</a>.</td>
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</tr>
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</table>
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<h3>Concept Model</h3>
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<p>The generator iterator class is a model of <a href=
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"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>.</p>
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<h3>Members</h3>
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<p>The generator iterator implements the member functions and operators
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required of the <a href=
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"http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>
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concept.<br></p>
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<hr>
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<h2><a name="make_generator_iterator" id="make_generator_iterator">The
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Generator Iterator Object Generator</a></h2>
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<p>The <tt>make_generator_iterator()</tt> function provides a convenient
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way to create generator iterator objects. The function saves the user the
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trouble of explicitly writing out the iterator types.</p>
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<blockquote>
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<pre>
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template <class Generator>
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typename generator_iterator_generator<Generator>::type
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make_generator_iterator(Generator & gen);
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</pre>
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</blockquote>
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<hr>
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<h3>Example</h3>
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<p>The following program shows how <code>generator_iterator</code>
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transforms a generator into an input iterator.</p>
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<blockquote>
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<pre>
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#include <iostream>
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#include <boost/generator_iterator.hpp>
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class my_generator
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{
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public:
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typedef int result_type;
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my_generator() : state(0) { }
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int operator()() { return ++state; }
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private:
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int state;
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};
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int main()
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{
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my_generator gen;
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boost::generator_iterator_generator<my_generator>::type it = boost::make_generator_iterator(gen);
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for(int i = 0; i < 10; ++i, ++it)
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std::cout << *it << std::endl;
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}
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</pre>
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</blockquote>
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<hr>
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<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
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"../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
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height="31" width="88"></a></p>
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<p>Revised
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<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
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<p><i>Copyright © 2001 <a href=
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"http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a></i></p>
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<p><i>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
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copy at <a href=
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"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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