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<title>Issue 476: Forward Iterator implied mutability</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">NAD</a> status.</em></p>
<h3 id="476"><a href="lwg-closed.html#476">476</a>. Forward Iterator implied mutability</h3>
<p><b>Section:</b> 24.3.5.5 <a href="https://wg21.link/forward.iterators">[forward.iterators]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2004-07-09 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#forward.iterators">issues</a> in [forward.iterators].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>

<p>24.1/3 says:</p>
<blockquote><p>
  Forward iterators satisfy all the requirements of the input and
  output iterators and can be used whenever either kind is specified
</p></blockquote>

<p>
The problem is that satisfying the requirements of output iterator
means that you can always assign *something* into the result of
dereferencing it.  That makes almost all non-mutable forward
iterators non-conforming.  I think we need to sever the refinement
relationship between forward iterator and output iterator.
</p>

<p>Related issue: <a href="lwg-defects.html#200" title="Forward iterator requirements don't allow constant iterators (Status: CD1)">200</a><sup><a href="https://cplusplus.github.io/LWG/issue200" title="Latest snapshot">(i)</a></sup>.  But this is not a dup.</p>



<p id="res-476"><b>Proposed resolution:</b></p>


<p><b>Rationale:</b></p>
<p>Yes, 24.1/3 does say that. But it's introductory material. The
precise specification is in 24.1.3, and the requrements table there is
right.  We don't need to fine-tune introductory wording.  (Especially
since this wording is likely to be changed as part of the iterator
overhaul.)</p> 





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