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<title>Issue 589: Requirements on iterators of member template functions of containers</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#CD1">CD1</a> status.</em></p>
<h3 id="589"><a href="lwg-defects.html#589">589</a>. Requirements on iterators of member template functions of containers</h3>
<p><b>Section:</b> 23.2 <a href="https://wg21.link/container.requirements">[container.requirements]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2006-08-02 <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#container.requirements">issues</a> in [container.requirements].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Duplicate of:</b> <a href="lwg-closed.html#536" title="Container iterator constructor and explicit convertibility (Status: Dup)">536</a></p>
<p><b>Discussion:</b></p>
<p>
There appears to be no requirements on the InputIterators used in sequences in 23.1.1 in
terms of their value_type, and the requirements in 23.1.2 appear to be overly strict
(requires InputIterator::value_type be the same type as the container's value_type).
</p>


<p id="res-589"><b>Proposed resolution:</b></p>
<p>
Change 23.1.1 p3:
</p>

<blockquote><p>
In Tables 82 and 83, <code>X</code> denotes a sequence class, <code>a</code> denotes a
value of <code>X</code>, <code>i</code> and <code>j</code> denote iterators satisfying input
iterator requirements <ins>and refer to elements <ins>implicitly
convertible to</ins> <code>value_type</code></ins>, <code>[i, j)</code> denotes a valid
range, <code>n</code> denotes a value of <code>X::size_type</code>, <code>p</code> denotes a
valid iterator to <code>a</code>, <code>q</code> denotes a valid dereferenceable
iterator to <code>a</code>, <code>[q1, q2)</code> denotes a valid range in <code>a</code>,
and <code>t</code> denotes a value of <code>X::value_type</code>.
</p></blockquote>

<p>
Change 23.1.2 p7:
</p>

<blockquote><p>
In Table 84, <code>X</code> is an associative container class, <code>a</code> is a value
of <code>X</code>, <code>a_uniq</code> is a value of <code>X</code> when <code>X</code> supports
unique keys, and <code>a_eq</code> is a value of <code>X</code> when <code>X</code> supports
multiple keys, <code>i</code> and <code>j</code> satisfy input iterator requirements and
refer to elements <del>of</del> <ins>implicitly convertible to</ins>
<code>value_type</code>, <code>[i, j)</code> is a valid range, <code>p</code> is a valid
iterator to <code>a</code>, <code>q</code> is a valid dereferenceable iterator to
<code>a</code>, <code>[q1, q2)</code> is a valid range in <code>a</code>, <code>t</code> is a
value of <code>X::value_type</code>, <code>k</code> is a value of <code>X::key_type</code>
and <code>c</code> is a value of type <code>X::key_compare</code>.
</p></blockquote>



<p><b>Rationale:</b></p>
<p>
Concepts will probably come in and rewrite this section anyway.  But just in case it is
easy to fix this up as a safety net and as a clear statement of intent.
</p>





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