boost-react-native-bundle

<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" /> <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" /> <meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003." /> <link rel="stylesheet" href="../../../rst.css" type="text/css" /> </head> <body> <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>    <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">   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>     <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>    <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>    </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>. 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