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Edits for committee meeting, moving algorithm changes to suggestions for WP.

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@ -7,7 +7,7 @@
<title>New Iterator Concepts</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="2003-09-22" />
<meta name="date" content="2003-10-16" />
<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved" />
<style type="text/css"><!--
@ -214,10 +214,12 @@ ul.auto-toc {
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first reference" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a>, <a class="reference" href="mailto:jsiek&#64;osl.iu.edu">jsiek&#64;osl.iu.edu</a>, <a class="last reference" href="mailto:witt&#64;acm.org">witt&#64;acm.org</a></td></tr>
<tr><th class="docinfo-name">Organization:</th>
<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 Lab</a>, University of Hanover <a class="last reference" href="http://www.ive.uni-hannover.de">Institute for Transport Railway Operation and Construction</a></td></tr>
<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 Lab</a>, University of Hanover <a class="last reference" 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>2003-09-22</td></tr>
<tr class="field"><th class="docinfo-name">Number:</th><td class="field-body">N1531=03-0114</td>
<td>2003-10-16</td></tr>
<tr class="field"><th class="docinfo-name">Number:</th><td class="field-body">N1530=03-0133</td>
</tr>
<tr><th class="docinfo-name">Copyright:</th>
<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved</td></tr>
@ -232,7 +234,7 @@ access and positioning independently. This allows the
concepts to more closely match the requirements
of algorithms and provides better categorizations
of iterators that are used in practice. This proposal
is a revision of paper <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2001/n1297.html">n1297</a> and <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1477.html">n1477</a>.</td>
is a revision of paper <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2001/n1297.html">n1297</a>, <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1477.html">n1477</a>, and <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1531.html">n1531</a>.</td>
</tr>
</tbody>
</table>
@ -240,29 +242,38 @@ is a revision of paper <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc
<p class="topic-title"><a name="table-of-contents">Table of Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#motivation" id="id1" name="id1">Motivation</a></li>
<li><a class="reference" href="#impact-on-the-standard" id="id2" name="id2">Impact on the Standard</a></li>
<li><a class="reference" href="#design" id="id3" name="id3">Design</a></li>
<li><a class="reference" href="#proposed-text" id="id4" name="id4">Proposed Text</a><ul>
<li><a class="reference" href="#addition-to-lib-iterator-requirements" id="id5" name="id5">Addition to [lib.iterator.requirements]</a><ul>
<li><a class="reference" href="#iterator-value-access-concepts-lib-iterator-value-access" id="id6" name="id6">Iterator Value Access Concepts [lib.iterator.value.access]</a><ul>
<li><a class="reference" href="#readable-iterators-lib-readable-iterators" id="id7" name="id7">Readable Iterators [lib.readable.iterators]</a></li>
<li><a class="reference" href="#writable-iterators-lib-writable-iterators" id="id8" name="id8">Writable Iterators [lib.writable.iterators]</a></li>
<li><a class="reference" href="#swappable-iterators-lib-swappable-iterators" id="id9" name="id9">Swappable Iterators [lib.swappable.iterators]</a></li>
<li><a class="reference" href="#lvalue-iterators-lib-lvalue-iterators" id="id10" name="id10">Lvalue Iterators [lib.lvalue.iterators]</a></li>
</ul>
</li>
<li><a class="reference" href="#iterator-traversal-concepts-lib-iterator-traversal" id="id11" name="id11">Iterator Traversal Concepts [lib.iterator.traversal]</a><ul>
<li><a class="reference" href="#incrementable-iterators-lib-incrementable-iterators" id="id12" name="id12">Incrementable Iterators [lib.incrementable.iterators]</a></li>
<li><a class="reference" href="#single-pass-iterators-lib-single-pass-iterators" id="id13" name="id13">Single Pass Iterators [lib.single.pass.iterators]</a></li>
<li><a class="reference" href="#forward-traversal-iterators-lib-forward-traversal-iterators" id="id14" name="id14">Forward Traversal Iterators [lib.forward.traversal.iterators]</a></li>
<li><a class="reference" href="#bidirectional-traversal-iterators-lib-bidirectional-traversal-iterators" id="id15" name="id15">Bidirectional Traversal Iterators [lib.bidirectional.traversal.iterators]</a></li>
<li><a class="reference" href="#random-access-traversal-iterators-lib-random-access-traversal-iterators" id="id16" name="id16">Random Access Traversal Iterators [lib.random.access.traversal.iterators]</a></li>
<li><a class="reference" href="#impact-on-the-standard" id="id2" name="id2">Impact on the Standard</a><ul>
<li><a class="reference" href="#proposed-changes-for-tr1" id="id3" name="id3">Proposed Changes for TR1</a></li>
<li><a class="reference" href="#possible-but-not-proposed-changes-to-the-working-paper" id="id4" name="id4">Possible (but not proposed) Changes to the Working Paper</a><ul>
<li><a class="reference" href="#changes-to-algorithm-requirements" id="id5" name="id5">Changes to Algorithm Requirements</a></li>
<li><a class="reference" href="#deprecations" id="id6" name="id6">Deprecations</a></li>
<li><a class="reference" href="#vector-bool" id="id7" name="id7"><tt class="literal"><span class="pre">vector&lt;bool&gt;</span></tt></a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference" href="#addition-to-lib-iterator-synopsis" id="id17" name="id17">Addition to [lib.iterator.synopsis]</a></li>
<li><a class="reference" href="#addition-to-lib-iterator-traits" id="id18" name="id18">Addition to [lib.iterator.traits]</a></li>
<li><a class="reference" href="#design" id="id8" name="id8">Design</a></li>
<li><a class="reference" href="#proposed-text" id="id9" name="id9">Proposed Text</a><ul>
<li><a class="reference" href="#addition-to-lib-iterator-requirements" id="id10" name="id10">Addition to [lib.iterator.requirements]</a><ul>
<li><a class="reference" href="#iterator-value-access-concepts-lib-iterator-value-access" id="id11" name="id11">Iterator Value Access Concepts [lib.iterator.value.access]</a><ul>
<li><a class="reference" href="#readable-iterators-lib-readable-iterators" id="id12" name="id12">Readable Iterators [lib.readable.iterators]</a></li>
<li><a class="reference" href="#writable-iterators-lib-writable-iterators" id="id13" name="id13">Writable Iterators [lib.writable.iterators]</a></li>
<li><a class="reference" href="#swappable-iterators-lib-swappable-iterators" id="id14" name="id14">Swappable Iterators [lib.swappable.iterators]</a></li>
<li><a class="reference" href="#lvalue-iterators-lib-lvalue-iterators" id="id15" name="id15">Lvalue Iterators [lib.lvalue.iterators]</a></li>
</ul>
</li>
<li><a class="reference" href="#iterator-traversal-concepts-lib-iterator-traversal" id="id16" name="id16">Iterator Traversal Concepts [lib.iterator.traversal]</a><ul>
<li><a class="reference" href="#incrementable-iterators-lib-incrementable-iterators" id="id17" name="id17">Incrementable Iterators [lib.incrementable.iterators]</a></li>
<li><a class="reference" href="#single-pass-iterators-lib-single-pass-iterators" id="id18" name="id18">Single Pass Iterators [lib.single.pass.iterators]</a></li>
<li><a class="reference" href="#forward-traversal-iterators-lib-forward-traversal-iterators" id="id19" name="id19">Forward Traversal Iterators [lib.forward.traversal.iterators]</a></li>
<li><a class="reference" href="#bidirectional-traversal-iterators-lib-bidirectional-traversal-iterators" id="id20" name="id20">Bidirectional Traversal Iterators [lib.bidirectional.traversal.iterators]</a></li>
<li><a class="reference" href="#random-access-traversal-iterators-lib-random-access-traversal-iterators" id="id21" name="id21">Random Access Traversal Iterators [lib.random.access.traversal.iterators]</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference" href="#addition-to-lib-iterator-synopsis" id="id22" name="id22">Addition to [lib.iterator.synopsis]</a></li>
<li><a class="reference" href="#addition-to-lib-iterator-traits" id="id23" name="id23">Addition to [lib.iterator.traits]</a></li>
</ul>
</li>
</ul>
@ -284,12 +295,15 @@ following table gives a summary of the current value access
requirements in the iterator categories.</p>
<table border class="table">
<colgroup>
<col width="31%" />
<col width="69%" />
<col width="39%" />
<col width="61%" />
</colgroup>
<thead valign="bottom">
<tr><th colspan="2">Value Access Requirements in Existing Iterator Categories</th>
</tr>
<tr><th>Existing Category</th>
<th>Requirement</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>Output Iterator</td>
@ -299,12 +313,13 @@ requirements in the iterator categories.</p>
<td><tt class="literal"><span class="pre">*i</span></tt> is convertible to <tt class="literal"><span class="pre">T</span></tt></td>
</tr>
<tr><td>Forward Iterator</td>
<td><tt class="literal"><span class="pre">*i</span></tt> is <tt class="literal"><span class="pre">T&amp;</span></tt> (or <tt class="literal"><span class="pre">const</span> <span class="pre">T&amp;</span></tt> once <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/lwg-active.html#200">issue 200</a>
is resolved)</td>
<td><tt class="literal"><span class="pre">*i</span></tt> is <tt class="literal"><span class="pre">T&amp;</span></tt> (or <tt class="literal"><span class="pre">const</span> <span class="pre">T&amp;</span></tt>
once <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/lwg-active.html#200">issue 200</a> is resolved)</td>
</tr>
<tr><td>Random Access Iterator</td>
<td><tt class="literal"><span class="pre">i[n]</span></tt> is convertible to <tt class="literal"><span class="pre">T</span></tt> (also <tt class="literal"><span class="pre">i[n]</span> <span class="pre">=</span> <span class="pre">t</span></tt>
is required for mutable iterators once <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/lwg-active.html#299">issue 299</a>
<td><tt class="literal"><span class="pre">i[n]</span></tt> is convertible to <tt class="literal"><span class="pre">T</span></tt>
(also <tt class="literal"><span class="pre">i[n]</span> <span class="pre">=</span> <span class="pre">t</span></tt> is required for
mutable iterators once <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/lwg-active.html#299">issue 299</a>
is resolved)</td>
</tr>
</tbody>
@ -350,6 +365,8 @@ traversal from the need for a true reference return type.</li>
</div>
<div class="section" id="impact-on-the-standard">
<h1><a class="toc-backref" href="#id2" name="impact-on-the-standard">Impact on the Standard</a></h1>
<div class="section" id="proposed-changes-for-tr1">
<h2><a class="toc-backref" href="#id3" name="proposed-changes-for-tr1">Proposed Changes for TR1</a></h2>
<p>The new iterator concepts are backward-compatible with the old
iterator requirements, and old iterators are forward-compatible with
the new iterator concepts. That is to say, iterators that satisfy the
@ -366,9 +383,18 @@ is convertible to input_iterator_tag? -JGS -->
<p>The algorithms in the standard library benefit from the new iterator
concepts because the new concepts provide a more accurate way to
express their type requirements. The result is algorithms that are
usable in more situations and have fewer type requirements. The
following lists the proposed changes to the type requirements of
algorithms.</p>
usable in more situations and have fewer type requirements.</p>
</div>
<div class="section" id="possible-but-not-proposed-changes-to-the-working-paper">
<h2><a class="toc-backref" href="#id4" name="possible-but-not-proposed-changes-to-the-working-paper">Possible (but not proposed) Changes to the Working Paper</a></h2>
<p>The extensions in this paper suggest several changes we might make
to the working paper for the next standard. These changes are not
a formal part of this proposal for TR1.</p>
<div class="section" id="changes-to-algorithm-requirements">
<h3><a class="toc-backref" href="#id5" name="changes-to-algorithm-requirements">Changes to Algorithm Requirements</a></h3>
<p>The following lists possible (but not proposed) changes to the type
requirements of algorithms, phrased as textual substitutions,
listing the algorithms to which each textual substitution applies.</p>
<p>Forward Iterator -&gt; Forward Traversal Iterator and Readable Iterator</p>
<blockquote>
<tt class="literal"><span class="pre">find_end,</span> <span class="pre">adjacent_find,</span> <span class="pre">search,</span> <span class="pre">search_n,</span> <span class="pre">rotate_copy,</span>
@ -424,8 +450,24 @@ Bidirectional Iterator (2) -&gt; Bidirectional Traversal Iterator and Writable I
<dd><tt class="literal"><span class="pre">transform</span></tt></dd>
</dl>
</div>
<div class="section" id="deprecations">
<h3><a class="toc-backref" href="#id6" name="deprecations">Deprecations</a></h3>
<p>For the next working paper (but not for TR1), the committee should
consider deprecating the old iterator tags, and
std::iterator_traits, since it will be superceded by individual
traits metafunctions.</p>
</div>
<div class="section" id="vector-bool">
<h3><a class="toc-backref" href="#id7" name="vector-bool"><tt class="literal"><span class="pre">vector&lt;bool&gt;</span></tt></a></h3>
<p>For the next working paper (but not for TR1), the committee should
consider reclassifying <tt class="literal"><span class="pre">vector&lt;bool&gt;::iterator</span></tt> as a Random
Access Traversal Iterator and Readable Iterator and Writable
Iterator.</p>
</div>
</div>
</div>
<div class="section" id="design">
<h1><a class="toc-backref" href="#id3" name="design">Design</a></h1>
<h1><a class="toc-backref" href="#id8" name="design">Design</a></h1>
<p>The iterator requirements are to be separated into two groups. One set
of concepts handles the syntax and semantics of value access:</p>
<ul class="simple">
@ -527,17 +569,17 @@ only required to return something convertible to the <tt class="literal"><span c
<tt class="literal"><span class="pre">i[n]</span> <span class="pre">=</span> <span class="pre">t</span></tt> (for a Writable Iterator).</p>
</div>
<div class="section" id="proposed-text">
<h1><a class="toc-backref" href="#id4" name="proposed-text">Proposed Text</a></h1>
<h1><a class="toc-backref" href="#id9" name="proposed-text">Proposed Text</a></h1>
<div class="section" id="addition-to-lib-iterator-requirements">
<h2><a class="toc-backref" href="#id5" name="addition-to-lib-iterator-requirements">Addition to [lib.iterator.requirements]</a></h2>
<h2><a class="toc-backref" href="#id10" name="addition-to-lib-iterator-requirements">Addition to [lib.iterator.requirements]</a></h2>
<div class="section" id="iterator-value-access-concepts-lib-iterator-value-access">
<h3><a class="toc-backref" href="#id6" name="iterator-value-access-concepts-lib-iterator-value-access">Iterator Value Access Concepts [lib.iterator.value.access]</a></h3>
<h3><a class="toc-backref" href="#id11" name="iterator-value-access-concepts-lib-iterator-value-access">Iterator Value Access Concepts [lib.iterator.value.access]</a></h3>
<p>In the tables below, <tt class="literal"><span class="pre">X</span></tt> is an iterator type, <tt class="literal"><span class="pre">a</span></tt> is a constant
object of type <tt class="literal"><span class="pre">X</span></tt>, <tt class="literal"><span class="pre">T</span></tt> is
<tt class="literal"><span class="pre">std::iterator_traits&lt;X&gt;::value_type</span></tt>, and <tt class="literal"><span class="pre">v</span></tt> is a constant
object of type <tt class="literal"><span class="pre">T</span></tt>.</p>
<a class="target" id="readable-iterator" name="readable-iterator"></a><div class="section" id="readable-iterators-lib-readable-iterators">
<h4><a class="toc-backref" href="#id7" name="readable-iterators-lib-readable-iterators">Readable Iterators [lib.readable.iterators]</a></h4>
<h4><a class="toc-backref" href="#id12" name="readable-iterators-lib-readable-iterators">Readable Iterators [lib.readable.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Readable Iterator</em> concept
for the value type <tt class="literal"><span class="pre">T</span></tt> if the following expressions are valid and
respect the stated semantics. <tt class="literal"><span class="pre">U</span></tt> is the type of any specified
@ -557,12 +599,13 @@ member of type <tt class="literal"><span class="pre">T</span></tt>.</p>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">iterator_traits&lt;X&gt;::value_type</span></tt></td>
<tr><td><tt class="literal"><span class="pre">iterator_traits&lt;</span> <span class="pre">X</span>
<span class="pre">&gt;::value_type</span></tt></td>
<td><tt class="literal"><span class="pre">T</span></tt></td>
<td>Any non-reference,
non-cv-qualified type</td>
</tr>
<tr><td><tt class="literal"><span class="pre">iterator_traits&lt;X&gt;::reference</span></tt></td>
<tr><td><tt class="literal"><span class="pre">iterator_traits&lt;</span> <span class="pre">X&gt;::reference</span></tt></td>
<td>Convertible to
<tt class="literal"><span class="pre">iterator_traits&lt;X&gt;::value_type</span></tt></td>
<td>&nbsp;</td>
@ -588,7 +631,7 @@ to <tt class="literal"><span class="pre">(*a).m</span></tt></td>
</table>
<a class="target" id="writable-iterator" name="writable-iterator"></a></div>
<div class="section" id="writable-iterators-lib-writable-iterators">
<h4><a class="toc-backref" href="#id8" name="writable-iterators-lib-writable-iterators">Writable Iterators [lib.writable.iterators]</a></h4>
<h4><a class="toc-backref" href="#id13" name="writable-iterators-lib-writable-iterators">Writable Iterators [lib.writable.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Writable Iterator</em> concept
if the following expressions are valid and respect the stated
semantics. In addition, a model of <em>Writable Iterator</em> must include
@ -623,7 +666,7 @@ value types of <tt class="literal"><span class="pre">X</span></tt></td>
</table>
</div>
<div class="section" id="swappable-iterators-lib-swappable-iterators">
<h4><a class="toc-backref" href="#id9" name="swappable-iterators-lib-swappable-iterators">Swappable Iterators [lib.swappable.iterators]</a></h4>
<h4><a class="toc-backref" href="#id14" name="swappable-iterators-lib-swappable-iterators">Swappable Iterators [lib.swappable.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Swappable Iterator</em> concept
if the following expressions are valid and respect the stated
semantics.</p>
@ -659,7 +702,7 @@ exchanged</td>
</dl>
</div>
<div class="section" id="lvalue-iterators-lib-lvalue-iterators">
<h4><a class="toc-backref" href="#id10" name="lvalue-iterators-lib-lvalue-iterators">Lvalue Iterators [lib.lvalue.iterators]</a></h4>
<h4><a class="toc-backref" href="#id15" name="lvalue-iterators-lib-lvalue-iterators">Lvalue Iterators [lib.lvalue.iterators]</a></h4>
<p>The <em>Lvalue Iterator</em> concept adds the requirement that the
<tt class="literal"><span class="pre">reference</span></tt> type be a reference to the value type of the iterator.</p>
<table border class="table">
@ -689,13 +732,13 @@ cv-qualification</td>
</div>
</div>
<div class="section" id="iterator-traversal-concepts-lib-iterator-traversal">
<h3><a class="toc-backref" href="#id11" name="iterator-traversal-concepts-lib-iterator-traversal">Iterator Traversal Concepts [lib.iterator.traversal]</a></h3>
<h3><a class="toc-backref" href="#id16" name="iterator-traversal-concepts-lib-iterator-traversal">Iterator Traversal Concepts [lib.iterator.traversal]</a></h3>
<p>In the tables below, <tt class="literal"><span class="pre">X</span></tt> is an iterator type, <tt class="literal"><span class="pre">a</span></tt> and <tt class="literal"><span class="pre">b</span></tt> are
constant objects of type <tt class="literal"><span class="pre">X</span></tt>, <tt class="literal"><span class="pre">r</span></tt> and <tt class="literal"><span class="pre">s</span></tt> are mutable objects of
type <tt class="literal"><span class="pre">X</span></tt>, <tt class="literal"><span class="pre">T</span></tt> is <tt class="literal"><span class="pre">std::iterator_traits&lt;X&gt;::value_type</span></tt>, and
<tt class="literal"><span class="pre">v</span></tt> is a constant object of type <tt class="literal"><span class="pre">T</span></tt>.</p>
<div class="section" id="incrementable-iterators-lib-incrementable-iterators">
<h4><a class="toc-backref" href="#id12" name="incrementable-iterators-lib-incrementable-iterators">Incrementable Iterators [lib.incrementable.iterators]</a></h4>
<h4><a class="toc-backref" href="#id17" name="incrementable-iterators-lib-incrementable-iterators">Incrementable Iterators [lib.incrementable.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Incrementable Iterator</em>
concept if the following expressions are valid and respect the stated
semantics.</p>
@ -738,7 +781,7 @@ semantics.</p>
</table>
</div>
<div class="section" id="single-pass-iterators-lib-single-pass-iterators">
<h4><a class="toc-backref" href="#id13" name="single-pass-iterators-lib-single-pass-iterators">Single Pass Iterators [lib.single.pass.iterators]</a></h4>
<h4><a class="toc-backref" href="#id18" name="single-pass-iterators-lib-single-pass-iterators">Single Pass Iterators [lib.single.pass.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Single Pass Iterator</em>
concept if the following expressions are valid and respect the stated
semantics.</p>
@ -784,7 +827,7 @@ relation over its domain</td>
</table>
</div>
<div class="section" id="forward-traversal-iterators-lib-forward-traversal-iterators">
<h4><a class="toc-backref" href="#id14" name="forward-traversal-iterators-lib-forward-traversal-iterators">Forward Traversal Iterators [lib.forward.traversal.iterators]</a></h4>
<h4><a class="toc-backref" href="#id19" name="forward-traversal-iterators-lib-forward-traversal-iterators">Forward Traversal Iterators [lib.forward.traversal.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Forward Traversal Iterator</em>
concept if the following expressions are valid and respect the stated
semantics.</p>
@ -831,14 +874,14 @@ the distance between iterators</td>
</table>
</div>
<div class="section" id="bidirectional-traversal-iterators-lib-bidirectional-traversal-iterators">
<h4><a class="toc-backref" href="#id15" name="bidirectional-traversal-iterators-lib-bidirectional-traversal-iterators">Bidirectional Traversal Iterators [lib.bidirectional.traversal.iterators]</a></h4>
<h4><a class="toc-backref" href="#id20" name="bidirectional-traversal-iterators-lib-bidirectional-traversal-iterators">Bidirectional Traversal Iterators [lib.bidirectional.traversal.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal
Iterator</em> concept if the following expressions are valid and respect
the stated semantics.</p>
<table border class="table">
<colgroup>
<col width="35%" />
<col width="44%" />
<col width="37%" />
<col width="42%" />
<col width="21%" />
</colgroup>
<thead valign="bottom">
@ -883,7 +926,7 @@ implies <tt class="literal"><span class="pre">r</span> <span class="pre">==</spa
</table>
</div>
<div class="section" id="random-access-traversal-iterators-lib-random-access-traversal-iterators">
<h4><a class="toc-backref" href="#id16" name="random-access-traversal-iterators-lib-random-access-traversal-iterators">Random Access Traversal Iterators [lib.random.access.traversal.iterators]</a></h4>
<h4><a class="toc-backref" href="#id21" name="random-access-traversal-iterators-lib-random-access-traversal-iterators">Random Access Traversal Iterators [lib.random.access.traversal.iterators]</a></h4>
<p>A class or built-in type <tt class="literal"><span class="pre">X</span></tt> models the <em>Random Access Traversal
Iterator</em> concept if the following expressions are valid and respect
the stated semantics. In the table below, <tt class="literal"><span class="pre">Distance</span></tt> is
@ -892,8 +935,8 @@ constant object of type <tt class="literal"><span class="pre">Distance</span></t
<table border class="table">
<colgroup>
<col width="31%" />
<col width="35%" />
<col width="18%" />
<col width="38%" />
<col width="15%" />
<col width="16%" />
</colgroup>
<thead valign="bottom">
@ -926,8 +969,8 @@ Precondition</th>
</tr>
<tr><td><tt class="literal"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">n</span></tt>, <tt class="literal"><span class="pre">n</span> <span class="pre">+</span> <span class="pre">a</span></tt></td>
<td><tt class="literal"><span class="pre">X</span></tt></td>
<td><tt class="literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span> <span class="pre">tmp</span>
<span class="pre">+=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
<td><tt class="literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span>
<span class="pre">tmp</span> <span class="pre">+=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
<td>&nbsp;</td>
</tr>
<tr><td><tt class="literal"><span class="pre">r</span> <span class="pre">-=</span> <span class="pre">n</span></tt></td>
@ -937,14 +980,15 @@ Precondition</th>
</tr>
<tr><td><tt class="literal"><span class="pre">a</span> <span class="pre">-</span> <span class="pre">n</span></tt></td>
<td><tt class="literal"><span class="pre">X</span></tt></td>
<td><tt class="literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span> <span class="pre">tmp</span>
<span class="pre">-=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
<td><tt class="literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span>
<span class="pre">tmp</span> <span class="pre">-=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
<td>&nbsp;</td>
</tr>
<tr><td><tt class="literal"><span class="pre">b</span> <span class="pre">-</span> <span class="pre">a</span></tt></td>
<td><tt class="literal"><span class="pre">Distance</span></tt></td>
<td><tt class="literal"><span class="pre">a</span> <span class="pre">&lt;</span> <span class="pre">b</span> <span class="pre">?</span>&nbsp; <span class="pre">distance(a,b)</span>
<span class="pre">:</span> <span class="pre">-distance(b,a)</span></tt></td>
<td><tt class="literal"><span class="pre">a</span> <span class="pre">&lt;</span> <span class="pre">b</span> <span class="pre">?</span>
<span class="pre">distance(a,b)</span> <span class="pre">:</span>
<span class="pre">-distance(b,a)</span></tt></td>
<td>pre: there exists a
value <tt class="literal"><span class="pre">n</span></tt> of
<tt class="literal"><span class="pre">Distance</span></tt> such that
@ -997,7 +1041,7 @@ ordering relation</td>
</div>
</div>
<div class="section" id="addition-to-lib-iterator-synopsis">
<h2><a class="toc-backref" href="#id17" name="addition-to-lib-iterator-synopsis">Addition to [lib.iterator.synopsis]</a></h2>
<h2><a class="toc-backref" href="#id22" name="addition-to-lib-iterator-synopsis">Addition to [lib.iterator.synopsis]</a></h2>
<pre class="literal-block">
// lib.iterator.traits, traits and tags
template &lt;class Iterator&gt; struct is_readable;
@ -1027,7 +1071,7 @@ struct input_output_iterator_tag : input_iterator_tag, output_iterator_tag {};
</pre>
</div>
<div class="section" id="addition-to-lib-iterator-traits">
<h2><a class="toc-backref" href="#id18" name="addition-to-lib-iterator-traits">Addition to [lib.iterator.traits]</a></h2>
<h2><a class="toc-backref" href="#id23" name="addition-to-lib-iterator-traits">Addition to [lib.iterator.traits]</a></h2>
<p>The <tt class="literal"><span class="pre">iterator_tag</span></tt> class template is an iterator category tag that
encodes the access enum and traversal tag in addition to being compatible
with the original iterator tags. The <tt class="literal"><span class="pre">iterator_tag</span></tt> class inherits
@ -1086,8 +1130,12 @@ is-writable(Iterator) =
cat = iterator_traits&lt;Iterator&gt;::iterator_category;
if (cat == iterator_tag&lt;Access,Traversal&gt;)
return Access &amp; writable_iterator;
else if (cat is convertible to forward_iterator_tag
or output_iterator_tag)
else if (cat is convertible to output_iterator_tag)
return true;
else if (
cat is convertible to forward_iterator_tag
and iterator_traits&lt;Iterator&gt;::reference is a
mutable reference)
return true;
else
return false;
@ -1157,7 +1205,7 @@ LocalWords: TraversalTag typename lvalues DWA Hmm JGS mis enum -->
<hr class="footer" />
<div class="footer">
<a class="reference" href="new-iter-concepts.rst">View document source</a>.
Generated on: 2003-09-22 19:48 UTC.
Generated on: 2003-10-30 20:56 UTC.
Generated by <a class="reference" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
</div>
</body>

121
doc/new-iter-concepts.rst
View File

@ -4,15 +4,18 @@
:Author: David Abrahams, Jeremy Siek, Thomas Witt
:Contact: dave@boost-consulting.com, jsiek@osl.iu.edu, witt@acm.org
:organization: `Boost Consulting`_, Indiana University `Open Systems Lab`_, University of Hanover `Institute for Transport Railway Operation and Construction`_
:organization: `Boost Consulting`_, Indiana University `Open
Systems Lab`_, University of Hanover `Institute for
Transport Railway Operation and Construction`_
:date: $Date$
:Number: revised from `N1531=03-0114`__
:Number: N1530=03-0133
:copyright: Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved
.. __: n1531_
.. _`Boost Consulting`: http://www.boost-consulting.com
.. _`Open Systems Lab`: http://www.osl.iu.edu
.. _`Institute for Transport Railway Operation and Construction`: http://www.ive.uni-hannover.de
.. _`Institute for Transport Railway Operation and Construction`:
http://www.ive.uni-hannover.de
:Abstract: We propose a new system of iterator concepts that treat
access and positioning independently. This allows the
@ -118,6 +121,9 @@ things happen:
Impact on the Standard
========================
Proposed Changes for TR1
========================
The new iterator concepts are backward-compatible with the old
iterator requirements, and old iterators are forward-compatible with
the new iterator concepts. That is to say, iterators that satisfy the
@ -134,12 +140,107 @@ appropriate old requirements.
a tag that is not input_iterator_tag but that
is convertible to input_iterator_tag? -JGS
The algorithms in the standard library could benefit from the new
iterator concepts because the new concepts provide a more accurate way
to express their type requirements. The result is algorithms that are
usable in more situations, have fewer type requirements, and that are
backward compatible. However, this proposal does not include making
these changes.
The algorithms in the standard library benefit from the new iterator
concepts because the new concepts provide a more accurate way to
express their type requirements. The result is algorithms that are
usable in more situations and have fewer type requirements.
Possible (but not proposed) Changes to the Working Paper
========================================================
The extensions in this paper suggest several changes we might make
to the working paper for the next standard. These changes are not
a formal part of this proposal for TR1.
Changes to Algorithm Requirements
+++++++++++++++++++++++++++++++++
For the next working paper (but not for TR1), the committee should
consider the following changes to the type requirements of
algorithms. These changes are phrased as phrased as textual
substitutions, listing the algorithms to which each textual
substitution applies.
Forward Iterator -> Forward Traversal Iterator and Readable Iterator
``find_end, adjacent_find, search, search_n, rotate_copy,
lower_bound, upper_bound, equal_range, binary_search,
min_element, max_element``
Forward Iterator (1) -> Single Pass Iterator and Readable Iterator,
Forward Iterator (2) -> Forward Traversal Iterator and Readable Iterator
``find_first_of``
Forward Iterator -> Readable Iterator and Writable Iterator
``iter_swap``
Forward Iterator -> Single Pass Iterator and Writable Iterator
``fill, generate``
Forward Iterator -> Forward Traversal Iterator and Swappable Iterator
``rotate``
Forward Iterator (1) -> Swappable Iterator and Single Pass Iterator,
Forward Iterator (2) -> Swappable Iterator and Incrementable Iterator
``swap_ranges``
Forward Iterator -> Forward Traversal Iterator and Readable Iterator and Writable Iterator
``remove, remove_if, unique``
Forward Iterator -> Single Pass Iterator and Readable Iterator and Writable Iterator
``replace, replace_if``
Bidirectional Iterator -> Bidirectional Traversal Iterator and Swappable Iterator
``reverse``
Bidirectional Iterator -> Bidirectional Traversal Iterator and Readable and Swappable Iterator
``partition``
Bidirectional Iterator (1) -> Bidirectional Traversal Iterator and Readable Iterator,
Bidirectional Iterator (2) -> Bidirectional Traversal Iterator and Writable Iterator
``copy_backwards``
Bidirectional Iterator -> Bidirectional Traversal Iterator and Swappable Iterator and Readable Iterator
``next_permutation, prev_permutation``
Bidirectional Iterator -> Bidirectional Traversal Iterator and Readable Iterator and Writable Iterator
``stable_partition, inplace_merge``
Bidirectional Iterator -> Bidirectional Traversal Iterator and Readable Iterator
``reverse_copy``
Random Access Iterator -> Random Access Traversal Iterator and Readable and Writable Iterator
``random_shuffle, sort, stable_sort, partial_sort, nth_element, push_heap, pop_heap
make_heap, sort_heap``
Input Iterator (2) -> Incrementable Iterator and Readable Iterator
``equal, mismatch``
Input Iterator (2) -> Incrementable Iterator and Readable Iterator
``transform``
Deprecations
++++++++++++
For the next working paper (but not for TR1), the committee should
consider deprecating the old iterator tags, and
std::iterator_traits, since it will be superceded by individual
traits metafunctions.
``vector<bool>``
++++++++++++++++
For the next working paper (but not for TR1), the committee should
consider reclassifying ``vector<bool>::iterator`` as a Random
Access Traversal Iterator and Readable Iterator and Writable
Iterator.
========
Design