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<title>Issue 1028: raw_storage_iterator needs to be a concept-constrained template</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#NAD_Concepts">NAD Concepts</a> status.</em></p>
<h3 id="1028"><a href="lwg-closed.html#1028">1028</a>. <code>raw_storage_iterator</code> needs to be a concept-constrained template</h3>
<p><b>Section:</b> 99 [depr.storage.iterator] <b>Status:</b> <a href="lwg-active.html#NAD_Concepts">NAD Concepts</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2017-06-15</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#depr.storage.iterator">issues</a> in [depr.storage.iterator].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p>
<p><b>Discussion:</b></p>

<p><b>Addresses UK 214 [CD1]</b></p>

<p>
<code>raw_storage_iterator</code> needs constraining as an iterator adaptor to be safely
used in constrained templates 
</p>

<p><i>[
Summit:
]</i></p>


<blockquote><p>
We look forward to a paper on this topic. We recommend no action until a
paper is available.
</p></blockquote>

<p><i>[
Post Summit Alisdair provided wording and rationale.
]</i></p>




<p id="res-1028"><b>Proposed resolution:</b></p>
<p>
20.2 <a href="https://wg21.link/memory">[memory]</a> p2
</p>
<p>
Update the synopsis for <code>&lt;memory&gt;</code>
</p>
<blockquote><pre>
// 20.7.8, raw storage iterator:
template &lt;<del>class</del> <ins>ForwardIterator</ins> Out<del>put</del>Iter<del>ator</del>, <del>class</del> <ins>ObjectType</ins> T&gt; 
  <ins>requires OutputIterator&lt; OutIter, T &gt;</ins>
    class raw_storage_iterator;

<ins>template &lt;ForwardIterator OutIter, ObjectType T&gt; 
  requires OutputIterator&lt; OutIter, T &gt;
  concept_map Iterator&lt;raw_storage_iterator&lt; OutIter, T &gt; &gt; { }</ins>
</pre></blockquote>


<p>
 [storage.iterator] p1
</p>
<p>
Replace class template definition with:
</p>
<blockquote><pre>
namespace std { 
  template &lt;<del>class</del> <ins>ForwardIterator</ins> Out<del>put</del>Iter<del>ator</del>, <del>class</del> <ins>ObjectType</ins> T&gt; 
    <ins>requires OutputIterator&lt; OutIter, T &gt;</ins>
  class raw_storage_iterator 
    : public iterator&lt;output_iterator_tag,void,void,void,void&gt; { 
  public: 
    explicit raw_storage_iterator(Out<del>put</del>Iter<del>ator</del> x); 

    raw_storage_iterator<del>&lt;OutputIterator,T&gt;</del>&amp; operator*(); 
    raw_storage_iterator<del>&lt;OutputIterator,T&gt;</del>&amp; operator=(const T&amp; element); 
    raw_storage_iterator<del>&lt;OutputIterator,T&gt;</del>&amp; operator++(); 
    raw_storage_iterator<del>&lt;OutputIterator,T&gt;</del> operator++(int); 
  }; 

  <ins>template &lt;ForwardIterator OutIter, ObjectType T&gt; 
    requires OutputIterator&lt; OutIter, T &gt;
    concept_map Iterator&lt;raw_storage_iterator&lt; OutIter, T &gt; &gt; { }</ins>
}
</pre></blockquote>


<p><b>Rationale:</b></p>
<p>
<code>raw_storage_iterator</code> has to adapt a <code>ForwardIterator</code>,
rather than just an <code>InputIterator</code> for two reasons:
</p>

<ol style="list-style-type:lower-roman">
<li>
The initial iterator passed by value is expected to remain valid,
pointing to the initialized region of memory.
</li>
<li>
to avoid breaking the declaration of post-increment operator which would
require some kind of proxy formulation to support generalised InputIterators.
</li>
</ol>






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