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<title>Issue 3732: prepend_range and append_range can't be amortized constant time</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++23">C++23</a> status.</em></p>
<h3 id="3732"><a href="lwg-defects.html#3732">3732</a>. <code>prepend_range</code> and <code>append_range</code> can't be amortized constant time</h3>
<p><b>Section:</b> 23.2.4 <a href="https://wg21.link/sequence.reqmts">[sequence.reqmts]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2022-07-06 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#sequence.reqmts">active issues</a> in [sequence.reqmts].</p>
<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
23.2.4 <a href="https://wg21.link/sequence.reqmts">[sequence.reqmts]</a>/69 says "An implementation shall implement them so as to take amortized constant time." 
followed by a list of operations that includes the newly added <code>append_range</code> and <code>prepend_range</code>. 
Obviously these operations cannot be implemented in amortized constant time.
<p/>
Because the actual complexity of these operations are already specified in the concrete container specification, 
we can just exclude them here.
</p>

<p><i>[2022-08-23; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>

<p><i>[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3732"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>

<li><p>Modify 23.2.4 <a href="https://wg21.link/sequence.reqmts">[sequence.reqmts]</a> as indicated:</p>

<blockquote>
<p>
-69- The following operations are provided for some types of sequence containers but not others. <del>An implementation
shall implement them</del><ins>Operations other than <code>prepend_range</code> and <code>append_range</code> are implemented</ins> 
so as to take amortized constant time.
</p>
</blockquote>
</li>


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