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<title>Iterator Archetype</title>
<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, Zephyr Associates, Inc." />
<meta name="date" content="2006-09-11" />
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<div class="document" id="iterator-archetype">
<h1 class="title">Iterator Archetype</h1>
<table class="docinfo" frame="void" rules="none">
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<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&#64;boost-consulting.com">dave&#64;boost-consulting.com</a>, <a class="reference external" href="mailto:jsiek&#64;osl.iu.edu">jsiek&#64;osl.iu.edu</a>, <a class="last reference external" href="mailto:witt&#64;styleadvisor.com">witt&#64;styleadvisor.com</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>, <a class="last reference external" href="http://www.styleadvisor.com">Zephyr Associates, Inc.</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 2004.</td></tr>
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<tr class="field"><th class="field-name">abstract:</th><td class="field-body">The <tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> class constructs a minimal implementation of
one of the iterator access concepts and one of the iterator traversal concepts.
This is used for doing a compile-time check to see if a the type requirements
of a template are really enough to cover the implementation of the template.
For further information see the documentation for the <a class="reference external" href="../../concept_check/index.html"><tt class="docutils literal"><span class="pre">boost::concept_check</span></tt></a> library.</td>
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<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="#reference" id="id1">Reference</a><ul>
<li><a class="reference internal" href="#iterator-archetype-synopsis" id="id2"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Synopsis</a></li>
<li><a class="reference internal" href="#access-category-tags" id="id3"><tt class="docutils literal"><span class="pre">Access</span> <span class="pre">Category</span> <span class="pre">Tags</span></tt></a></li>
<li><a class="reference internal" href="#iterator-archetype-requirements" id="id4"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Requirements</a></li>
<li><a class="reference internal" href="#iterator-archetype-models" id="id5"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Models</a></li>
<li><a class="reference internal" href="#traits" id="id6"><tt class="docutils literal"><span class="pre">Traits</span></tt></a></li>
</ul>
</li>
</ul>
</div>
<div class="section" id="reference">
<h1><a class="toc-backref" href="#id1">Reference</a></h1>
<div class="section" id="iterator-archetype-synopsis">
<h2><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Synopsis</a></h2>
<pre class="literal-block">
namespace iterator_archetypes
{
    // Access categories

    typedef /*implementation  defined*/ readable_iterator_t;
    typedef /*implementation  defined*/ writable_iterator_t;
    typedef /*implementation  defined*/ readable_writable_iterator_t;
    typedef /*implementation  defined*/ readable_lvalue_iterator_t;
    typedef /*implementation  defined*/ writable_lvalue_iterator_t;

}

template &lt;
    class Value
  , class AccessCategory
  , class TraversalCategory
&gt;
class iterator_archetype
{
    typedef /* see below */ value_type;
    typedef /* see below */ reference;
    typedef /* see below */ pointer;
    typedef /* see below */ difference_type;
    typedef /* see below */ iterator_category;
};
</pre>
</div>
<div class="section" id="access-category-tags">
<h2><a class="toc-backref" href="#id3"><tt class="docutils literal"><span class="pre">Access</span> <span class="pre">Category</span> <span class="pre">Tags</span></tt></a></h2>
<p>The access category types provided correspond to the following
standard iterator access concept combinations:</p>
<pre class="literal-block">
readable_iterator_t :=

  Readable Iterator

writable_iterator_t :=

  Writeable Iterator

readable_writable_iterator_t :=

  Readable Iterator &amp; Writeable Iterator &amp; Swappable Iterator

readable_lvalue_iterator_t :=

  Readable Iterator &amp; Lvalue Iterator

writeable_lvalue_iterator_t :=

  Readable Iterator &amp; Writeable Iterator &amp; Swappable Iterator &amp; Lvalue Iterator
</pre>
</div>
<div class="section" id="iterator-archetype-requirements">
<h2><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Requirements</a></h2>
<p>The <tt class="docutils literal"><span class="pre">AccessCategory</span></tt> argument must be one of the predefined access
category tags. The <tt class="docutils literal"><span class="pre">TraversalCategory</span></tt> must be one of the standard
traversal tags. The <tt class="docutils literal"><span class="pre">Value</span></tt> type must satisfy the requirements of
the iterator concept specified by <tt class="docutils literal"><span class="pre">AccessCategory</span></tt> and
<tt class="docutils literal"><span class="pre">TraversalCategory</span></tt> as implied by the nested traits types.</p>
</div>
<div class="section" id="iterator-archetype-models">
<h2><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> Models</a></h2>
<p><tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> models the iterator concepts specified by the
<tt class="docutils literal"><span class="pre">AccessCategory</span></tt> and <tt class="docutils literal"><span class="pre">TraversalCategory</span></tt>
arguments. <tt class="docutils literal"><span class="pre">iterator_archetype</span></tt> does not model any other access
concepts or any more derived traversal concepts.</p>
</div>
<div class="section" id="traits">
<h2><a class="toc-backref" href="#id6"><tt class="docutils literal"><span class="pre">Traits</span></tt></a></h2>
<p>The nested trait types are defined as follows:</p>
<pre class="literal-block">
if (AccessCategory == readable_iterator_t)

  value_type = Value
  reference  = Value
  pointer    = Value*

else if (AccessCategory == writable_iterator_t)

  value_type = void
  reference  = void
  pointer    = void

else if (AccessCategory == readable_writable_iterator_t)

  value_type = Value

  reference :=

    A type X that is convertible to Value for which the following
    expression is valid. Given an object x of type X and v of type
    Value.

    x = v

  pointer    = Value*

else if (AccessCategory == readable_lvalue_iterator_t)

  value_type = Value
  reference  = Value const&amp;
  pointer    = Value const*

else if (AccessCategory == writable_lvalue_iterator_t)

  value_type = Value
  reference  = Value&amp;
  pointer    = Value*

if ( TraversalCategory is convertible to forward_traversal_tag )

  difference_type := ptrdiff_t

else

  difference_type := unspecified type


iterator_category :=

  A type X satisfying the following two constraints:

     1. X is convertible to X1, and not to any more-derived
        type, where X1 is defined by:

          if (reference is a reference type
              &amp;&amp; TraversalCategory is convertible to forward_traversal_tag)
          {
              if (TraversalCategory is convertible to random_access_traversal_tag)
                  X1 = random_access_iterator_tag
              else if (TraversalCategory is convertible to bidirectional_traversal_tag)
                  X1 = bidirectional_iterator_tag
              else
                  X1 = forward_iterator_tag
          }
          else
          {
              if (TraversalCategory is convertible to single_pass_traversal_tag
                  &amp;&amp; reference != void)
                  X1 = input_iterator_tag
              else
                  X1 = output_iterator_tag
          }

     2. X is convertible to TraversalCategory
</pre>
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