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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.3.1: http://docutils.sourceforge.net/" />
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<title>Iterator Adaptor</title>
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<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
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<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
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<meta name="date" content="2003-09-14" />
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<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved" />
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<link rel="stylesheet" href="default.css" type="text/css" />
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</head>
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<body>
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<div class="document" id="iterator-adaptor">
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<h1 class="title">Iterator Adaptor</h1>
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<table class="docinfo" frame="void" rules="none">
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<col class="docinfo-name" />
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<col class="docinfo-content" />
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<tbody valign="top">
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<tr><th class="docinfo-name">Author:</th>
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<td>David Abrahams, Jeremy Siek, Thomas Witt</td></tr>
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<tr><th class="docinfo-name">Contact:</th>
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<td><a class="first reference" href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a>, <a class="reference" href="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</a>, <a class="last reference" href="mailto:witt@ive.uni-hannover.de">witt@ive.uni-hannover.de</a></td></tr>
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<tr><th class="docinfo-name">Organization:</th>
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<td><a class="first reference" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="reference" href="http://www.osl.iu.edu">Open Systems
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Lab</a>, University of Hanover <a class="last reference" href="http://www.ive.uni-hannover.de">Institute for Transport
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Railway Operation and Construction</a></td></tr>
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<tr><th class="docinfo-name">Date:</th>
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<td>2003-09-14</td></tr>
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<tr><th class="docinfo-name">Copyright:</th>
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<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved</td></tr>
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</tbody>
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</table>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">abstract:</th><td class="field-body"></td>
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</tr>
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</tbody>
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</table>
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<!-- Version 1.1 of this ReStructuredText document corresponds to
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n1530_, the paper accepted by the LWG. -->
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<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
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rights reserved -->
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<p>Each specialization of the <tt class="literal"><span class="pre">iterator_adaptor</span></tt> class template is derived from
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a specialization of <tt class="literal"><span class="pre">iterator_facade</span></tt>. The core interface functions
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expected by <tt class="literal"><span class="pre">iterator_facade</span></tt> are implemented in terms of the
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<tt class="literal"><span class="pre">iterator_adaptor</span></tt>'s <tt class="literal"><span class="pre">Base</span></tt> template parameter. A class derived
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from <tt class="literal"><span class="pre">iterator_adaptor</span></tt> typically redefines some of the core
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interface functions to adapt the behavior of the <tt class="literal"><span class="pre">Base</span></tt> type.
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Whether the derived class models any of the standard iterator concepts
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depends on the operations supported by the <tt class="literal"><span class="pre">Base</span></tt> type and which
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core interface functions of <tt class="literal"><span class="pre">iterator_facade</span></tt> are redefined in the
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<tt class="literal"><span class="pre">Derived</span></tt> class.</p>
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<div class="contents topic" id="table-of-contents">
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<p class="topic-title"><a name="table-of-contents">Table of Contents</a></p>
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<ul class="simple">
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<li><a class="reference" href="#introduction" id="id3" name="id3">Introduction</a></li>
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<li><a class="reference" href="#reference" id="id4" name="id4">Reference</a><ul>
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<li><a class="reference" href="#iterator-adaptor-base-class-parameters" id="id5" name="id5"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> base class parameters</a></li>
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<li><a class="reference" href="#iterator-adaptor-usage" id="id6" name="id6"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> usage</a></li>
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<li><a class="reference" href="#iterator-adaptor-public-operations" id="id7" name="id7"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> public operations</a></li>
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<li><a class="reference" href="#iterator-adaptor-protected-member-functions" id="id8" name="id8"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> protected member functions</a></li>
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<li><a class="reference" href="#iterator-adaptor-private-member-functions" id="id9" name="id9"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> private member functions</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="section" id="introduction">
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<h1><a class="toc-backref" href="#id3" name="introduction">Introduction</a></h1>
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<!-- Version 1.2 of this ReStructuredText document corresponds to
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n1530_, the paper accepted by the LWG for TR1. -->
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<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
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rights reserved -->
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<p>The <tt class="literal"><span class="pre">iterator_adaptor</span></tt> class template adapts some <tt class="literal"><span class="pre">Base</span></tt> <a class="footnote-reference" href="#base" id="id1" name="id1"><sup>1</sup></a>
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type to create a new iterator. Instantiations of <tt class="literal"><span class="pre">iterator_adaptor</span></tt>
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are derived from a corresponding instantiation of <tt class="literal"><span class="pre">iterator_facade</span></tt>
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and implement the core behaviors in terms of the <tt class="literal"><span class="pre">Base</span></tt> type. In
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essence, <tt class="literal"><span class="pre">iterator_adaptor</span></tt> merely forwards all operations to an
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instance of the <tt class="literal"><span class="pre">Base</span></tt> type, which it stores as a member.</p>
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<table class="footnote" frame="void" id="base" rules="none">
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<colgroup><col class="label" /><col /></colgroup>
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<tbody valign="top">
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<tr><td class="label"><a class="fn-backref" href="#id1" name="base">[1]</a></td><td>The term "Base" here does not refer to a base class and is
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not meant to imply the use of derivation. We have followed the lead
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of the standard library, which provides a base() function to access
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the underlying iterator object of a <tt class="literal"><span class="pre">reverse_iterator</span></tt> adaptor.</td></tr>
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</tbody>
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</table>
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<p>The user of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> creates a class derived from an
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instantiation of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> and then selectively
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redefines some of the core member functions described in the table
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above. The <tt class="literal"><span class="pre">Base</span></tt> type need not meet the full requirements for an
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iterator. It need only support the operations used by the core
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interface functions of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> that have not been
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redefined in the user's derived class.</p>
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<p>Several of the template parameters of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> default
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to <tt class="literal"><span class="pre">use_default</span></tt>. This allows the
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user to make use of a default parameter even when she wants to
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specify a parameter later in the parameter list. Also, the
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defaults for the corresponding associated types are somewhat
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complicated, so metaprogramming is required to compute them, and
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<tt class="literal"><span class="pre">use_default</span></tt> can help to simplify the implementation. Finally,
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the identity of the <tt class="literal"><span class="pre">use_default</span></tt> type is not left unspecified
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because specification helps to highlight that the <tt class="literal"><span class="pre">Reference</span></tt>
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template parameter may not always be identical to the iterator's
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<tt class="literal"><span class="pre">reference</span></tt> type, and will keep users from making mistakes based on
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that assumption.</p>
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</div>
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<div class="section" id="reference">
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<h1><a class="toc-backref" href="#id4" name="reference">Reference</a></h1>
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<!-- Version 1.4 of this ReStructuredText document corresponds to
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n1530_, the paper accepted by the LWG for TR1. -->
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<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
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rights reserved. -->
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<pre class="literal-block">
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template <
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class Derived
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, class Base
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, class Value = use_default
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, class CategoryOrTraversal = use_default
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, class Reference = use_default
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, class Difference = use_default
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>
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class iterator_adaptor
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: public iterator_facade<Derived, <em>V</em>, <em>C</em>, <em>R</em>, <em>D</em>> // see <a class="reference" href="#base-parameters">details</a>
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{
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friend class iterator_core_access;
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public:
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iterator_adaptor();
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explicit iterator_adaptor(Base iter);
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Base base() const;
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protected:
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Base const& base_reference() const;
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Base& base_reference();
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private: // Core iterator interface for iterator_facade.
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typename iterator_adaptor::reference dereference() const;
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template <
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class OtherDerived, class OtherIterator, class V, class C, class R, class D
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>
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bool equal(iterator_adaptor<OtherDerived, OtherIterator, V, C, R, D> const& x) const;
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void advance(typename iterator_adaptor::difference_type n);
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void increment();
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void decrement();
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template <
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class OtherDerived, class OtherIterator, class V, class C, class R, class D
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>
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typename iterator_adaptor::difference_type distance_to(
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iterator_adaptor<OtherDerived, OtherIterator, V, C, R, D> const& y) const;
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private:
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Base m_iterator; // exposition only
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};
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</pre>
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<a class="target" id="base-parameters" name="base-parameters"></a><div class="section" id="iterator-adaptor-base-class-parameters">
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<h2><a class="toc-backref" href="#id5" name="iterator-adaptor-base-class-parameters"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> base class parameters</a></h2>
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<p>The <em>V</em>, <em>C</em>, <em>R</em>, and <em>D</em> parameters of the <tt class="literal"><span class="pre">iterator_facade</span></tt>
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used as a base class in the summary of <tt class="literal"><span class="pre">iterator_adaptor</span></tt>
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above are defined as follows:</p>
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<pre class="literal-block">
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<em>V</em> = if (Value is use_default)
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return iterator_traits<Base>::value_type
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else
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return Value
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<em>C</em> = if (CategoryOrTraversal is use_default)
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return iterator_traversal<Base>::type
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else
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return CategoryOrTraversal
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<em>R</em> = if (Reference is use_default)
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if (Value is use_default)
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return iterator_traits<Base>::reference
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else
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return Value&
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else
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return Reference
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<em>D</em> = if (Difference is use_default)
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return iterator_traits<Base>::difference_type
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else
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return Difference
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</pre>
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</div>
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<div class="section" id="iterator-adaptor-usage">
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<h2><a class="toc-backref" href="#id6" name="iterator-adaptor-usage"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> usage</a></h2>
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<p>The <tt class="literal"><span class="pre">Derived</span></tt> template parameter must be a publicly derived from
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<tt class="literal"><span class="pre">iterator_adaptor</span></tt>. In order for <tt class="literal"><span class="pre">Derived</span></tt> to model the
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iterator concepts corresponding to
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<tt class="literal"><span class="pre">iterator_traits<Derived>::iterator_category</span></tt>, the expressions
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involving <tt class="literal"><span class="pre">m_iterator</span></tt> in the specifications of those private
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member functions of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> that may be called by
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<tt class="literal"><span class="pre">iterator_facade<Derived,</span> <span class="pre">V,</span> <span class="pre">C,</span> <span class="pre">R,</span> <span class="pre">D></span></tt>
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in evaluating any valid expression involving <tt class="literal"><span class="pre">Derived</span></tt>
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in those concepts' requirements.</p>
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</div>
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<div class="section" id="iterator-adaptor-public-operations">
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<h2><a class="toc-backref" href="#id7" name="iterator-adaptor-public-operations"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> public operations</a></h2>
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<p><tt class="literal"><span class="pre">iterator_adaptor();</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Requires:</th><td class="field-body">The <tt class="literal"><span class="pre">Base</span></tt> type must be Default Constructible.</td>
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</tr>
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> with
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<tt class="literal"><span class="pre">m_iterator</span></tt> default constructed.</td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">explicit</span> <span class="pre">iterator_adaptor(Base</span> <span class="pre">iter);</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">iterator_adaptor</span></tt> with
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<tt class="literal"><span class="pre">m_iterator</span></tt> copy constructed from <tt class="literal"><span class="pre">iter</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">Base</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="literal"><span class="pre">m_iterator</span></tt></td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="iterator-adaptor-protected-member-functions">
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<h2><a class="toc-backref" href="#id8" name="iterator-adaptor-protected-member-functions"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> protected member functions</a></h2>
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<p><tt class="literal"><span class="pre">Base</span> <span class="pre">const&</span> <span class="pre">base_reference()</span> <span class="pre">const;</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body">A const reference to <tt class="literal"><span class="pre">m_iterator</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">Base&</span> <span class="pre">base_reference();</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body">A non-const reference to <tt class="literal"><span class="pre">m_iterator</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="iterator-adaptor-private-member-functions">
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<h2><a class="toc-backref" href="#id9" name="iterator-adaptor-private-member-functions"><tt class="literal"><span class="pre">iterator_adaptor</span></tt> private member functions</a></h2>
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<p><tt class="literal"><span class="pre">typename</span> <span class="pre">iterator_adaptor::reference</span> <span class="pre">dereference()</span> <span class="pre">const;</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="literal"><span class="pre">*m_iterator</span></tt></td>
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</tr>
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</tbody>
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</table>
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<pre class="literal-block">
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template <
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class OtherDerived, class OtherIterator, class V, class C, class R, class D
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>
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bool equal(iterator_adaptor<OtherDerived, OtherIterator, V, C, R, D> const& x) const;
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</pre>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="literal"><span class="pre">m_iterator</span> <span class="pre">==</span> <span class="pre">x.base()</span></tt></td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">void</span> <span class="pre">advance(typename</span> <span class="pre">iterator_adaptor::difference_type</span> <span class="pre">n);</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="literal"><span class="pre">m_iterator</span> <span class="pre">+=</span> <span class="pre">n;</span></tt></td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">void</span> <span class="pre">increment();</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="literal"><span class="pre">++m_iterator;</span></tt></td>
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</tr>
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</tbody>
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</table>
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<p><tt class="literal"><span class="pre">void</span> <span class="pre">decrement();</span></tt></p>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="literal"><span class="pre">--m_iterator;</span></tt></td>
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</tr>
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</tbody>
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</table>
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<pre class="literal-block">
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template <
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class OtherDerived, class OtherIterator, class V, class C, class R, class D
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>
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typename iterator_adaptor::difference_type distance_to(
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iterator_adaptor<OtherDerived, OtherIterator, V, C, R, D> const& y) const;
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</pre>
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<table class="field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="literal"><span class="pre">y.base()</span> <span class="pre">-</span> <span class="pre">m_iterator</span></tt></td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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</div>
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<hr class="footer" />
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<div class="footer">
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<a class="reference" href="iterator_adaptor.rst">View document source</a>.
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Generated on: 2004-01-12 15:49 UTC.
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