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<title>Issue 367: remove_copy/remove_copy_if and Input Iterators</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="367"><a href="lwg-closed.html#367">367</a>. remove_copy/remove_copy_if and Input Iterators</h3>
<p><b>Section:</b> 26.7.8 <a href="https://wg21.link/alg.remove">[alg.remove]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Anthony Williams <b>Opened:</b> 2002-05-13 <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#alg.remove">issues</a> in [alg.remove].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
remove_copy and remove_copy_if (26.7.8 <a href="https://wg21.link/alg.remove">[alg.remove]</a>) permit their
input range to be marked with Input Iterators. However, since two
operations are required against the elements to copy (comparison and
assigment), when the input range uses Input Iterators, a temporary
copy must be taken to avoid dereferencing the iterator twice. This
therefore requires the value type of the InputIterator to be
CopyConstructible. If the iterators are at least Forward Iterators,
then the iterator can be dereferenced twice, or a reference to the
result maintained, so the temporary is not required.
</p>


<p id="res-367"><b>Proposed resolution:</b></p>
<p>
Add "If InputIterator does not meet the requirements of forward
iterator, then the value type of InputIterator must be copy
constructible. Otherwise copy constructible is not required." to
26.7.8 <a href="https://wg21.link/alg.remove">[alg.remove]</a> paragraph 6.
</p>


<p><b>Rationale:</b></p>
<p>The assumption is that an input iterator can't be dereferenced
  twice.  There's no basis for that assumption in the Standard.</p>





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