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<title>Issue 4277: &sect;[algorithms.requirements] It is unclear what an algorithm is</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#New">New</a> status.</em></p>
<h3 id="4277"><a href="lwg-active.html#4277">4277</a>. &sect;[algorithms.requirements] It is unclear what an algorithm is</h3>
<p><b>Section:</b> 26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Jan Schultke <b>Opened:</b> 2025-06-08 <b>Last modified:</b> 2025-06-14</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#algorithms.requirements">active issues</a> in [algorithms.requirements].</p>
<p><b>View all other</b> <a href="lwg-index.html#algorithms.requirements">issues</a> in [algorithms.requirements].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a> paragraph 15 states:
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<p>
The well-formedness and behavior of a call to an algorithm with an explicitly-specified 
template argument list is unspecified, except where explicitly stated otherwise.
</p>
</blockquote>
<p>
It is unclear what this applies to because "algorithm" is never defined. 26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a> 
paragraph 1 uses the term while mentioning iterators and containers, but  [algorithm] specifies 
function templates such as <code class='backtick'>std::gcd</code> which do not accept iterators.
<p/>
The <i>Remarks</i> specifications in 26.8.9 <a href="https://wg21.link/alg.min.max">[alg.min.max]</a> providing exemptions from 
26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a> paragraph 15 suggest that even function templates not 
accepting iterators are considered algorithms.
</p>


<p id="res-4277"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N5008" title=" Working Draft, Programming Languages — C++">N5008</a>.
</p>

<ol>
<li><p>Modify 26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a> as indicated:</p>

<blockquote>
<p>
-15- The well-formedness and behavior of a call to <del>an algorithm</del><ins>a function template specified in Clause 
26 <a href="https://wg21.link/algorithms">[algorithms]</a> (including call operators of algorithm function objects denoted as algorithms throughout Clause 
26.2 <a href="https://wg21.link/algorithms.requirements">[algorithms.requirements]</a>)</ins> with an explicitly-specified template argument list is unspecified, 
except where explicitly stated otherwise.
<p/>
[<i>Note 3</i>: Consequently, an implementation can declare an algorithm with different template parameters than those
presented. &mdash; <i>end note</i>]
</p>
</blockquote>
</li>

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