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<title>Issue 1278: Inconsistent return values for forward_list::insert_after</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#C++11">C++11</a> status.</em></p>
<h3 id="1278"><a href="lwg-defects.html#1278">1278</a>. Inconsistent return values for <code>forward_list::insert_after</code></h3>
<p><b>Section:</b> 23.3.7.5 <a href="https://wg21.link/forward.list.modifiers">[forward.list.modifiers]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Bo Persson <b>Opened:</b> 2009-11-25 <b>Last modified:</b> 2023-02-07</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#forward.list.modifiers">issues</a> in [forward.list.modifiers].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
After applying LDR<a href="lwg-defects.html#149" title="Insert should return iterator to first element inserted (Status: C++11)">149</a><sup><a href="https://cplusplus.github.io/LWG/issue149" title="Latest snapshot">(i)</a></sup>, <code>forward_list</code> now has 5
overloads of <code>insert_after</code>, all returning an iterator.
</p>

<p>
However, two of those - inserting a single object - return "An iterator
pointing to a copy of <code>x</code> [the inserted object]" while the other
three - inserting zero or more objects - return an iterator equivalent
to the position parameter, pointing before any possibly inserted
objects.
</p>

<p>
Is this the intended change? 
</p>

<p>
I don't really know what <code>insert_after(position, empty_range)</code>
should really return, but always returning <code>position</code> seems less
than useful.
</p>

<p><i>[
2010-02-04 Howard adds:
]</i></p>


<blockquote>
<p>
I agree this inconsistency will be error prone and needs to be fixed. 
Additionally <code>emplace_after</code>'s return value is unspecified.
</p>
</blockquote>

<p><i>[
2010-02-04 Nico provides wording.
]</i></p>


<p><i>[
2010 Pittsburgh:
]</i></p>


<blockquote><p>
We prefer to return an iterator to the last inserted element.  Modify the
proposed wording and then set to Ready.
</p></blockquote>

<p><i>[
2010-03-15 Howard adds:
]</i></p>


<blockquote><p>
Wording updated and set to Ready.
</p></blockquote>



<p id="res-1278"><b>Proposed resolution:</b></p>
<p>
In <code>forward_list</code> modifiers  [forwardlist.modifiers]
make the following modifications:
</p>

<blockquote>
<pre>
iterator insert_after(const_iterator position, size_type n, const T&amp; x);
</pre>
<blockquote>
<p>...</p>
<p>
10 <i>Returns:</i> <del>position.</del> <ins>An iterator pointing to the last
inserted copy of <code>x</code> or <code>position</code> if <code>n == 0</code>.</ins>
</p>
</blockquote>

<pre>
template &lt;class InputIterator&gt;
  iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
</pre>
<blockquote>
<p>...</p>

<p>
13 <i>Returns:</i> <del>position.</del> <ins>An iterator pointing to the last
inserted element or <code>position</code> if <code>first == last</code>.</ins>
</p>
</blockquote>

<pre>
iterator insert_after(const_iterator position, initializer_list&lt;T&gt; il);
</pre>
<blockquote>
<p>...</p>

<p>
15 <i>Returns:</i> <del>position.</del> <ins>An iterator pointing to the last
inserted element or <code>position</code> if <code>il</code> is empty.</ins>
</p>
</blockquote>

<pre>
template &lt;class... Args&gt;
  iterator emplace_after(const_iterator position, Args&amp;&amp;... args);
</pre>
<blockquote>
<p>...</p>
<p>17 ...</p>

<p><ins>
<i>Returns:</i> An iterator pointing to the new constructed element from
args.
</ins></p>
</blockquote>

</blockquote>






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