<?xml version="1.0"?>
<concept name="ForwardIterator" category="Iterator"><!--
Based on concepts from the SGI Standard Template Library documentation:
Copyright (c) 1996-1999
Silicon Graphics Computer Systems, Inc.

Copyright (c) 1994
Hewlett-Packard Company
--><!--
Copyright 2000-2001 University of Notre Dame du Lac.
Copyright 2001-2002 Indiana University.
Some concepts based on versions from the MTL draft manual and Boost Graph
and Property Map documentation:
Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000
-->
<!--
Permission to use, copy, modify, distribute and
sell this software and its documentation for any purpose is
hereby granted without fee, provided that the above copyright
notice appears in all copies and that both that copyright
notice and this permission notice appear in supporting
documentation.  Silicon Graphics makes no representations
about the suitability of this software for any purpose.  It is
provided "as is" without express or implied
warranty.
-->
  <param name="Iter" role="iterator-type"/>

  <use-header name="iterator"/>

  <models-sentence>The iterator type <arg num="1"/> must be a model of <self/>.</models-sentence>

  <description>
  <para>A forward iterator is an iterator that can read through a sequence of
  values.  It is multi-pass (old values of the iterator can be
  re-used), and can be either mutable (data pointed to by it can be
  changed) or not mutable.</para>

  <para>An iterator represents a position in a sequence.  Therefore, the
  iterator can point into the sequence (returning a value when dereferenced
  and being incrementable), or be off-the-end (and not dereferenceable or
  incrementable).</para>
  </description>

  <associated-type name="value_type">
    <get-member-type name="value_type">
      <apply-template name="std::iterator_traits">
	<type name="Iter"/>
      </apply-template>
    </get-member-type>
    <description><simpara>The value type of the iterator</simpara></description>
  </associated-type>

  <refines const="no" concept="InputIterator"/>
  <refines const="no" concept="OutputIterator"/>

<!-- DPG doesn't understand this
  <models const="no" testable="yes" concept="Input Iterator">
    <type name="Iter"/>
  </models>
-->
<!--
  <models-when-mutable concept="Output Iterator">
    <type name="Iter"/>
    <type name="value_type"/>
  </models-when-mutable>
-->

  <notation variables="i j">
    <sample-value>
      <type name="Iter"/>
    </sample-value>
  </notation>

  <associated-type name="category">
    <get-member-type name="iterator_category">
      <apply-template name="std::iterator_traits">
	<type name="Iter"/>
      </apply-template>
    </get-member-type>
    <description><simpara>The category of the iterator</simpara></description>
  </associated-type>

  <notation variables="x">
    <sample-value>
      <type name="value_type"/>
    </sample-value>
  </notation>

  <valid-type-expression name="Category tag">
    <description/>
    <type name="category"/>
    <return-type>
      <derived-from testable="yes">
	<type name="std::forward_iterator_tag"/>
      </derived-from>
    </return-type>
  </valid-type-expression>

  <valid-expression name="Dereference">
    <dereference>
      <sample-value><type name="Iter"/></sample-value>
    </dereference>
    <return-type>
      <require-same-type testable="yes">
	<const-if-not-mutable>
	  <reference-to><type name="value_type"/></reference-to>
	</const-if-not-mutable>
      </require-same-type>
    </return-type>
    <precondition><code>i</code> is incrementable (not
    off-the-end)</precondition>
  </valid-expression>

  <valid-expression name="Member access">
    <pointer-member>
      <sample-value><type name="Iter"/></sample-value>
    </pointer-member>
    <return-type>
      <require-same-type testable="yes">
	<const-if-not-mutable>
	  <pointer-to><type name="value_type"/></pointer-to>
	</const-if-not-mutable>
      </require-same-type>
    </return-type>
    <precondition><code>i</code> is incrementable (not
    off-the-end)</precondition>
  </valid-expression>

  <valid-expression name="Preincrement">
    <preincrement>
      <sample-value><reference-to><type name="Iter"/></reference-to></sample-value>
    </preincrement>
    <return-type>
      <require-same-type testable="yes">
	<reference-to><type name="Iter"/></reference-to>
      </require-same-type>
    </return-type>
    <precondition><code>i</code> is incrementable (not
    off-the-end)</precondition>
  </valid-expression>

  <valid-expression name="Postincrement">
    <postincrement>
      <sample-value><reference-to><type name="Iter"/></reference-to></sample-value>
    </postincrement>
    <return-type>
      <require-same-type testable="yes"><type name="Iter"/></require-same-type>
    </return-type>
    <precondition><code>i</code> is incrementable (not
    off-the-end)</precondition>
    <semantics>Equivalent to <code>{Iter j = i; ++i; return j;}</code></semantics>
    <postcondition><code>i</code> is dereferenceable or
    off-the-end</postcondition>
  </valid-expression>

  <complexity>
  All iterator operations must take amortized constant time.
  </complexity>

  <invariant name="Predecrement must return object">
  <code>&amp;i = &amp;(++i)</code>
  </invariant>

  <invariant name="Unique path through sequence">
  <code>i == j</code> implies <code>++i == ++j</code>
  </invariant>

  <example-model>
    <pointer-to>
      <type name="T"/>
    </pointer-to>
  </example-model>

  <example-model>
    <get-member-type name="iterator">
      <apply-template name="std::hash_set">
	<type name="T"/>
      </apply-template>
    </get-member-type>
  </example-model>

  <see-also concept="BidirectionalIterator"/>

</concept>
