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<title>Issue 1210: Iterator reachability should not require a container</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#Resolved">Resolved</a> status.</em></p>
<h3 id="1210"><a href="lwg-defects.html#1210">1210</a>. Iterator reachability should not require a container</h3>
<p><b>Section:</b> 24.3 <a href="https://wg21.link/iterator.requirements">[iterator.requirements]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-09-18 <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#iterator.requirements">issues</a> in [iterator.requirements].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
p6 Iterator requirements 24.3 <a href="https://wg21.link/iterator.requirements">[iterator.requirements]</a>
</p>

<blockquote><p>
An iterator <code>j</code> is called reachable from an iterator <code>i</code> if and only if
there is a finite sequence of applications of the expression <code>++i</code> that
makes <code>i == j</code>. If <code>j</code> is reachable from <code>i</code>, they refer to the same
container.
</p></blockquote>

<p>
A good example would be stream iterators, which do not refer to a
container.  Typically, the end iterator from a range of stream iterators
will compare equal for many such ranges.  I suggest striking the second
sentence.
</p>

<p>
An alternative wording might be:
</p>

<blockquote><p>
If <code>j</code> is reachable from <code>i</code>, and both <code>i</code> and
<code>j</code> are dereferencable iterators, then they refer to the same
range.
</p></blockquote>

<p><i>[
2010 Pittsburgh:  Moved to <del>NAD Editorial</del><ins>Resolved</ins>.  Rationale added below.
]</i></p>




<p><b>Rationale:</b></p>
<p>
Solved by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a>.
</p>


<p id="res-1210"><b>Proposed resolution:</b></p>
<p>
Change 24.3 <a href="https://wg21.link/iterator.requirements">[iterator.requirements]</a>, p6:
</p>

<blockquote><p>
An iterator <code>j</code> is called <i>reachable</i> from an iterator
<code>i</code> if and only if there is a finite sequence of applications of
the expression <code>++i</code> that makes <code>i == j</code>. <del>If
<code>j</code> is reachable from <code>i</code>, they refer to the same
container.</del>
</p></blockquote>





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