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<title>Wording for range-based for-loop</title>
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<div class="document" id="wording-for-range-based-for-loop">
<h1 class="title">Wording for range-based for-loop</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>Thorsten Ottosen</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference" href="mailto:tottosen&#64;dezide.com">tottosen&#64;dezide.com</a></td></tr>
<tr class="field"><th class="docinfo-name">Advisor:</th><td class="field-body">Lawrence Crowl</td>
</tr>
<tr class="field"><th class="docinfo-name">organizations:</th><td class="field-body">Dezide Aps</td>
</tr>
<tr><th class="docinfo-name">Date:</th>
<td>2006-02-18</td></tr>
<tr class="field"><th class="docinfo-name">Number:</th><td class="field-body">WG21/N1961 and J16/06-0031</td>
</tr>
<tr class="field"><th class="docinfo-name">Working Group:</th><td class="field-body">Core</td>
</tr>
</tbody>
</table>
<div class="abstract topic">
<p class="topic-title first">Abstract</p>
<p>This paper provides wording for the new range-based for-loop 
previously described in <a class="reference" href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1868.html">n1868</a></p>
</div>
<!-- ######################### -->
<!-- # Roles -->
<!-- ######################### -->
<div class="contents topic">
<p class="topic-title first"><a id="table-of-contents" name="table-of-contents">Table of Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#introduction" id="id1" name="id1">Introduction</a></li>
<li><a class="reference" href="#the-range-based-for-statement" id="id2" name="id2">6.5.4 The range-based <tt class="docutils literal"><span class="pre">for</span></tt> statement</a></li>
<li><a class="reference" href="#header-iterator-synopsis" id="id3" name="id3">24.2 Header <tt class="docutils literal"><span class="pre">&lt;iterator&gt;</span></tt> synopsis</a></li>
<li><a class="reference" href="#range-primitives" id="id4" name="id4">24.5.6 Range primitives</a><ul>
<li><a class="reference" href="#range-operations" id="id5" name="id5">24.5.6.1 Range operations</a></li>
</ul>
</li>
<li><a class="reference" href="#a-grammar-summary" id="id6" name="id6">A Grammar summary</a></li>
</ul>
</div>
<!-- section-numbering: -->
<div class="section">
<h1><a class="toc-backref" href="#id1" id="introduction" name="introduction">Introduction</a></h1>
<p>Each numbered section below describes a new section
for the standard or modifications to an existing section.
Comments are written in <strong>bold</strong> and are not part of the wording.</p>
<p>The author would like to thank Lawrence Crowl for his help. Any mistake
is the responsibility of the author.</p>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id2" id="the-range-based-for-statement" name="the-range-based-for-statement">6.5.4 The range-based <tt class="docutils literal docutils literal"><span class="pre">for</span></tt> statement</a></h1>
<p>1 The range-based <tt class="docutils literal"><span class="pre">for</span></tt> statement</p>
<pre class="literal-block">
for( <em>type-specifier-seq</em> <em>simple-declarator</em> : <em>expression</em> ) <em>statement</em>
</pre>
<p>is syntactically equivalent to</p>
<pre class="literal-block">
{
     auto&amp;&amp;  __rng(( <em>expression</em> ));
    
     for( auto __begin( std::begin(__rng) ), __end( std::end(__rng) );
          __begin != __end; ++__begin )
     {
         <em>type-specifier-seq</em> <em>simple-declarator</em> ( *__begin );
         <em>statement</em>
     }    
}
</pre>
<p>where <tt class="docutils literal"><span class="pre">__rng</span></tt>, <tt class="docutils literal"><span class="pre">__begin</span></tt> and <tt class="docutils literal"><span class="pre">__end</span></tt> are implementation-defined local variables.</p>
<p>2 If the header <tt class="docutils literal"><span class="pre">&lt;iterator&gt;</span></tt> (24.2) is not included prior to a use of the range-based <tt class="docutils literal"><span class="pre">for</span></tt> statement, 
the program is ill-formed.</p>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id3" id="header-iterator-synopsis" name="header-iterator-synopsis">24.2 Header <tt class="docutils literal docutils literal"><span class="pre">&lt;iterator&gt;</span></tt> synopsis</a></h1>
<p><strong>Add the following to the end within namespace 'std'</strong>:</p>
<pre class="literal-block">
template&lt; class T &gt;
auto range_begin( T&amp;&amp; t ) -&gt; decltype( t.begin() );

template&lt; class T &gt;
T range_begin( const pair&lt;T,T&gt;&amp; p ) ;

template&lt; class T, size_t N &gt;
T* range_begin( T (&amp;array)[N] ) 

template&lt; class T &gt;
auto begin( T&amp;&amp; t ) -&gt; decltype( range_begin(t) );

template&lt; class T &gt;
auto range_end( T&amp;&amp; t ) -&gt; decltype( t.end() );

template&lt; class T &gt;
T range_end( const pair&lt;T,T&gt;&amp; p );

template&lt; class T, size_t N &gt;
T* range_end( T (&amp;array)[N] );

template&lt; class T &gt;
auto end( T&amp;&amp; t ) -&gt; decltype( range_end(t) );
</pre>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id4" id="range-primitives" name="range-primitives">24.5.6 Range primitives</a></h1>
<p>1 To support the range-based <tt class="docutils literal"><span class="pre">for</span></tt> statement (6.5.4), the library provides
several utility functions.</p>
<div class="section">
<h2><a class="toc-backref" href="#id5" id="range-operations" name="range-operations">24.5.6.1 Range operations</a></h2>
<p>1 The functions <tt class="docutils literal"><span class="pre">range_begin()</span></tt> and <tt class="docutils literal"><span class="pre">range_begin()</span></tt> are intended to be overloaded for a 
user-defined type <tt class="docutils literal"><span class="pre">T</span></tt> in the namespace of <tt class="docutils literal"><span class="pre">T</span></tt>.</p>
<p>2 Within the standard library, the functions <tt class="docutils literal"><span class="pre">begin()</span></tt> and <tt class="docutils literal"><span class="pre">end()</span></tt> are
always called qualified with the <tt class="docutils literal"><span class="pre">std</span></tt> namespace.</p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">auto</span> <span class="pre">range_begin(</span> <span class="pre">T&amp;&amp;</span> <span class="pre">t</span> <span class="pre">)</span> <span class="pre">-&gt;</span> <span class="pre">decltype(</span> <span class="pre">t.begin()</span> <span class="pre">);</span></tt></p>
<p>3 <em>Returns:</em> <tt class="docutils literal"><span class="pre">t.begin()</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">T</span> <span class="pre">range_begin(</span> <span class="pre">const</span> <span class="pre">pair&lt;T,T&gt;&amp;</span> <span class="pre">p</span> <span class="pre">);</span></tt></p>
<p>4 <em>Returns:</em> <tt class="docutils literal"><span class="pre">p.first</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T,</span> <span class="pre">size_t</span> <span class="pre">N</span> <span class="pre">&gt;</span>
<span class="pre">T*</span> <span class="pre">range_begin(</span> <span class="pre">T</span> <span class="pre">(&amp;array)[N]</span> <span class="pre">);</span></tt></p>
<p>5 <em>Returns:</em> <tt class="docutils literal"><span class="pre">array</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">auto</span> <span class="pre">begin(</span> <span class="pre">T&amp;&amp;</span> <span class="pre">t</span> <span class="pre">)</span> <span class="pre">-&gt;</span> <span class="pre">decltype(</span> <span class="pre">range_begin(t)</span> <span class="pre">);</span></tt></p>
<p>6 <em>Returns:</em>  <tt class="docutils literal"><span class="pre">range_begin(t)</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">auto</span> <span class="pre">range_end(</span> <span class="pre">T&amp;&amp;</span> <span class="pre">t</span> <span class="pre">)</span> <span class="pre">-&gt;</span> <span class="pre">decltype(</span> <span class="pre">t.end()</span> <span class="pre">);</span></tt></p>
<p>7 <em>Returns:</em> <tt class="docutils literal"><span class="pre">t.end()</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">T</span> <span class="pre">range_end(</span> <span class="pre">const</span> <span class="pre">pair&lt;T,T&gt;&amp;</span> <span class="pre">p</span> <span class="pre">);</span></tt></p>
<p>8 <em>Returns:</em> <tt class="docutils literal"><span class="pre">p.second</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T,</span> <span class="pre">size_t</span> <span class="pre">N</span> <span class="pre">&gt;</span>
<span class="pre">T*</span> <span class="pre">range_end(</span> <span class="pre">T</span> <span class="pre">(&amp;array)[N]</span> <span class="pre">);</span></tt></p>
<p>9 <em>Returns:</em> <tt class="docutils literal"><span class="pre">array</span> <span class="pre">+</span> <span class="pre">N</span></tt></p>
<p><tt class="docutils literal"><span class="pre">template&lt;</span> <span class="pre">class</span> <span class="pre">T</span> <span class="pre">&gt;</span>
<span class="pre">auto</span> <span class="pre">end(</span> <span class="pre">T&amp;&amp;</span> <span class="pre">t</span> <span class="pre">)</span> <span class="pre">-&gt;</span> <span class="pre">decltype(</span> <span class="pre">range_end(t)</span> <span class="pre">);</span></tt></p>
<p>10 <em>Returns:</em>  <tt class="docutils literal"><span class="pre">range_end(t)</span></tt></p>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id6" id="a-grammar-summary" name="a-grammar-summary">A Grammar summary</a></h1>
<p><strong>Add the following to section A.7 after the rule for 'declarator'</strong></p>
<pre class="literal-block">
<em>simple-declarator:</em>
    <em>declarator-id</em>
    <em>ptr-operator</em> <em>simple-declarator</em>
</pre>
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