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151 lines
4.0 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<title>Generator Iterator Adaptor Documentation</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="center" width="277" height="86">
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<h1>Generator Iterator Adaptor</h1>
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Defined in header <a href="../../boost/generator_iterator.hpp">boost/generator_iterator.hpp</a>
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<p>
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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
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takes a
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<a href="http://www.sgi.com/tech/stl/Generator.html">Generator</a>
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and creates a model of
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<a href="http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>.
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Each increment retrieves an item from the generator and makes it
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available to be retrieved by dereferencing. The motivation for this
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iterator is that some concepts can be more naturally expressed as a
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generator, while most STL algorithms expect an iterator. An example
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is the <a href="../random/index.html">Random Number</a> library.
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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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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
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this class is the Generator function object type that is being
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wrapped. The generator iterator adaptor only holds a reference (or
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pointer) to the function object, therefore the function object must
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outlive the generator iterator adaptor constructed from it.
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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 <a href="iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...> 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>
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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="http://www.sgi.com/tech/stl/Generator.html">Generator</a></tt>
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<td>The generator (0-ary function object) type being
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wrapped. The 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
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of
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<a href="http://www.sgi.com/tech/stl/Generator.html">Generator</a>.
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</td>
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</table>
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<h3>Concept Model</h3>
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The generator iterator class is a model of
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<a href="http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>.
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<h3>Members</h3>
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The generator iterator implements the member functions
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and operators required of the
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<a href="http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>
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concept.
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<br>
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<hr>
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<h2><a name="make_generator_iterator">The Generator Iterator Object Generator</a></h2>
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The <tt>make_generator_iterator()</tt> function provides a
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convenient way to create generator iterator objects. The function
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saves the user the trouble of explicitly writing out the iterator
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types.
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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_function_output_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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The following program shows how <code>generator_iterator</code>
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transforms a generator into an input iterator.
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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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Written by Jens Maurer.
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</body>
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</html>
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