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- <title>Transform Iterator</title>
- <meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
- <meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
- <meta name="date" content="2006-09-11" />
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- <div class="document" id="transform-iterator">
- <h1 class="title">Transform Iterator</h1>
- <table class="docinfo" frame="void" rules="none">
- <col class="docinfo-name" />
- <col class="docinfo-content" />
- <tbody valign="top">
- <tr><th class="docinfo-name">Author:</th>
- <td>David Abrahams, Jeremy Siek, Thomas Witt</td></tr>
- <tr><th class="docinfo-name">Contact:</th>
- <td><a class="first reference external" href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a>, <a class="reference external" href="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</a>, <a class="last reference external" href="mailto:witt@ive.uni-hannover.de">witt@ive.uni-hannover.de</a></td></tr>
- <tr><th class="docinfo-name">Organization:</th>
- <td><a class="first reference external" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="reference external" href="http://www.osl.iu.edu">Open Systems
- Lab</a>, University of Hanover <a class="last reference external" href="http://www.ive.uni-hannover.de">Institute for Transport
- Railway Operation and Construction</a></td></tr>
- <tr><th class="docinfo-name">Date:</th>
- <td>2006-09-11</td></tr>
- <tr><th class="docinfo-name">Copyright:</th>
- <td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.</td></tr>
- </tbody>
- </table>
- <!-- Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">abstract:</th><td class="field-body"><!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- The transform iterator adapts an iterator by modifying the
- <tt class="docutils literal"><span class="pre">operator*</span></tt> to apply a function object to the result of
- dereferencing the iterator and returning the result.</td>
- </tr>
- </tbody>
- </table>
- <div class="contents topic" id="table-of-contents">
- <p class="topic-title first">Table of Contents</p>
- <ul class="simple">
- <li><a class="reference internal" href="#transform-iterator-synopsis" id="id2"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> synopsis</a></li>
- <li><a class="reference internal" href="#transform-iterator-requirements" id="id3"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> requirements</a></li>
- <li><a class="reference internal" href="#transform-iterator-models" id="id4"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</a></li>
- <li><a class="reference internal" href="#transform-iterator-operations" id="id5"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> operations</a></li>
- <li><a class="reference internal" href="#example" id="id6">Example</a></li>
- </ul>
- </div>
- <div class="section" id="transform-iterator-synopsis">
- <h1><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> synopsis</a></h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <!-- Version 1.3 of this document was accepted for TR1 -->
- <pre class="literal-block">
- template <class UnaryFunction,
- class Iterator,
- class Reference = use_default,
- class Value = use_default>
- class transform_iterator
- {
- public:
- typedef /* see below */ value_type;
- typedef /* see below */ reference;
- typedef /* see below */ pointer;
- typedef iterator_traits<Iterator>::difference_type difference_type;
- typedef /* see below */ iterator_category;
- transform_iterator();
- transform_iterator(Iterator const& x, UnaryFunction f);
- template<class F2, class I2, class R2, class V2>
- transform_iterator(
- transform_iterator<F2, I2, R2, V2> const& t
- , typename enable_if_convertible<I2, Iterator>::type* = 0 // exposition only
- , typename enable_if_convertible<F2, UnaryFunction>::type* = 0 // exposition only
- );
- UnaryFunction functor() const;
- Iterator const& base() const;
- reference operator*() const;
- transform_iterator& operator++();
- transform_iterator& operator--();
- private:
- Iterator m_iterator; // exposition only
- UnaryFunction m_f; // exposition only
- };
- </pre>
- <p>If <tt class="docutils literal"><span class="pre">Reference</span></tt> is <tt class="docutils literal"><span class="pre">use_default</span></tt> then the <tt class="docutils literal"><span class="pre">reference</span></tt> member of
- <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> is
- <tt class="docutils literal"><span class="pre">result_of<const UnaryFunction(iterator_traits<Iterator>::reference)>::type</span></tt>.
- Otherwise, <tt class="docutils literal"><span class="pre">reference</span></tt> is <tt class="docutils literal"><span class="pre">Reference</span></tt>.</p>
- <p>If <tt class="docutils literal"><span class="pre">Value</span></tt> is <tt class="docutils literal"><span class="pre">use_default</span></tt> then the <tt class="docutils literal"><span class="pre">value_type</span></tt> member is
- <tt class="docutils literal"><span class="pre">remove_cv<remove_reference<reference></span> <span class="pre">>::type</span></tt>. Otherwise,
- <tt class="docutils literal"><span class="pre">value_type</span></tt> is <tt class="docutils literal"><span class="pre">Value</span></tt>.</p>
- <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and if <tt class="docutils literal"><span class="pre">Iterator</span></tt>
- models Random Access Traversal Iterator, then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
- convertible to <tt class="docutils literal"><span class="pre">random_access_iterator_tag</span></tt>. Otherwise, if
- <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Bidirectional Traversal Iterator, then
- <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
- <tt class="docutils literal"><span class="pre">bidirectional_iterator_tag</span></tt>. Otherwise <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
- convertible to <tt class="docutils literal"><span class="pre">forward_iterator_tag</span></tt>. If <tt class="docutils literal"><span class="pre">Iterator</span></tt> does not
- model Readable Lvalue Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
- convertible to <tt class="docutils literal"><span class="pre">input_iterator_tag</span></tt>.</p>
- </div>
- <div class="section" id="transform-iterator-requirements">
- <h1><a class="toc-backref" href="#id3"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> requirements</a></h1>
- <p>The type <tt class="docutils literal"><span class="pre">UnaryFunction</span></tt> must be Assignable, Copy Constructible, and
- the expression <tt class="docutils literal"><span class="pre">f(*i)</span></tt> must be valid where <tt class="docutils literal"><span class="pre">f</span></tt> is a const object of
- type <tt class="docutils literal"><span class="pre">UnaryFunction</span></tt>, <tt class="docutils literal"><span class="pre">i</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Iterator</span></tt>, and
- where the type of <tt class="docutils literal"><span class="pre">f(*i)</span></tt> must be
- <tt class="docutils literal"><span class="pre">result_of<const UnaryFunction(iterator_traits<Iterator>::reference)>::type</span></tt>.</p>
- <p>The argument <tt class="docutils literal"><span class="pre">Iterator</span></tt> shall model Readable Iterator.</p>
- </div>
- <div class="section" id="transform-iterator-models">
- <h1><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</a></h1>
- <p>The resulting <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models the most refined of the
- following that is also modeled by <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</p>
- <blockquote>
- <ul class="simple">
- <li>Writable Lvalue Iterator if <tt class="docutils literal"><span class="pre">transform_iterator::reference</span></tt> is a non-const reference.</li>
- <li>Readable Lvalue Iterator if <tt class="docutils literal"><span class="pre">transform_iterator::reference</span></tt> is a const reference.</li>
- <li>Readable Iterator otherwise.</li>
- </ul>
- </blockquote>
- <p>The <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models the most refined standard traversal
- concept that is modeled by the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument.</p>
- <p>If <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> is a model of Readable Lvalue Iterator then
- it models the following original iterator concepts depending on what
- the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument models.</p>
- <table border="1" class="docutils">
- <colgroup>
- <col width="47%" />
- <col width="53%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
- <th class="head">then <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td>Single Pass Iterator</td>
- <td>Input Iterator</td>
- </tr>
- <tr><td>Forward Traversal Iterator</td>
- <td>Forward Iterator</td>
- </tr>
- <tr><td>Bidirectional Traversal Iterator</td>
- <td>Bidirectional Iterator</td>
- </tr>
- <tr><td>Random Access Traversal Iterator</td>
- <td>Random Access Iterator</td>
- </tr>
- </tbody>
- </table>
- <p>If <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models Writable Lvalue Iterator then it is a
- mutable iterator (as defined in the old iterator requirements).</p>
- <p><tt class="docutils literal"><span class="pre">transform_iterator<F1,</span> <span class="pre">X,</span> <span class="pre">R1,</span> <span class="pre">V1></span></tt> is interoperable with
- <tt class="docutils literal"><span class="pre">transform_iterator<F2,</span> <span class="pre">Y,</span> <span class="pre">R2,</span> <span class="pre">V2></span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is
- interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
- </div>
- <div class="section" id="transform-iterator-operations">
- <h1><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> operations</a></h1>
- <p>In addition to the operations required by the concepts modeled by
- <tt class="docutils literal"><span class="pre">transform_iterator</span></tt>, <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> provides the following
- operations.</p>
- <p><tt class="docutils literal"><span class="pre">transform_iterator();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
- and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> default constructed.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">transform_iterator(Iterator</span> <span class="pre">const&</span> <span class="pre">x,</span> <span class="pre">UnaryFunction</span> <span class="pre">f);</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
- initialized to <tt class="docutils literal"><span class="pre">f</span></tt> and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template<class F2, class I2, class R2, class V2>
- transform_iterator(
- transform_iterator<F2, I2, R2, V2> const& t
- , typename enable_if_convertible<I2, Iterator>::type* = 0 // exposition only
- , typename enable_if_convertible<F2, UnaryFunction>::type* = 0 // exposition only
- );
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
- initialized to <tt class="docutils literal"><span class="pre">t.functor()</span></tt> and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to
- <tt class="docutils literal"><span class="pre">t.base()</span></tt>.</td>
- </tr>
- <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">OtherIterator</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">UnaryFunction</span> <span class="pre">functor()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_f</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">const&</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_f(*m_iterator)</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">transform_iterator&</span> <span class="pre">operator++();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_iterator</span></tt></td>
- </tr>
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">transform_iterator&</span> <span class="pre">operator--();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_iterator</span></tt></td>
- </tr>
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
- </tr>
- </tbody>
- </table>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <pre class="literal-block">
- template <class UnaryFunction, class Iterator>
- transform_iterator<UnaryFunction, Iterator>
- make_transform_iterator(Iterator it, UnaryFunction fun);
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator<UnaryFunction,</span> <span class="pre">Iterator></span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
- initialized to <tt class="docutils literal"><span class="pre">f</span></tt> and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template <class UnaryFunction, class Iterator>
- transform_iterator<UnaryFunction, Iterator>
- make_transform_iterator(Iterator it);
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator<UnaryFunction,</span> <span class="pre">Iterator></span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
- default constructed and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- </div>
- <div class="section" id="example">
- <h1><a class="toc-backref" href="#id6">Example</a></h1>
- <p>This is a simple example of using the transform_iterators class to
- generate iterators that multiply (or add to) the value returned by
- dereferencing the iterator. It would be cooler to use lambda library
- in this example.</p>
- <pre class="literal-block">
- int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
- const int N = sizeof(x)/sizeof(int);
- typedef boost::binder1st< std::multiplies<int> > Function;
- typedef boost::transform_iterator<Function, int*> doubling_iterator;
- doubling_iterator i(x, boost::bind1st(std::multiplies<int>(), 2)),
- i_end(x + N, boost::bind1st(std::multiplies<int>(), 2));
- std::cout << "multiplying the array by 2:" << std::endl;
- while (i != i_end)
- std::cout << *i++ << " ";
- std::cout << std::endl;
- std::cout << "adding 4 to each element in the array:" << std::endl;
- std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus<int>(), 4)),
- boost::make_transform_iterator(x + N, boost::bind1st(std::plus<int>(), 4)),
- std::ostream_iterator<int>(std::cout, " "));
- std::cout << std::endl;
- </pre>
- <p>The output is:</p>
- <pre class="literal-block">
- multiplying the array by 2:
- 2 4 6 8 10 12 14 16
- adding 4 to each element in the array:
- 5 6 7 8 9 10 11 12
- </pre>
- <p>The source code for this example can be found <a class="reference external" href="../example/transform_iterator_example.cpp">here</a>.</p>
- </div>
- </div>
- <div class="footer">
- <hr class="footer" />
- <a class="reference external" href="transform_iterator.rst">View document source</a>.
- Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
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