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<title>Issue 3439: "Distance" template parameter is underspecified</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="3439"><a href="lwg-active.html#3439">3439</a>. "<code>Distance</code>" template parameter is underspecified</h3>
<p><b>Section:</b> 24.4.3 <a href="https://wg21.link/iterator.operations">[iterator.operations]</a>, 26.7.12 <a href="https://wg21.link/alg.random.sample">[alg.random.sample]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Jens Maurer <b>Opened:</b> 2020-05-01 <b>Last modified:</b> 2020-05-09</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#iterator.operations">active issues</a> in [iterator.operations].</p>
<p><b>View all other</b> <a href="lwg-index.html#iterator.operations">issues</a> in [iterator.operations].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The library specification conveys pre-concept requirements on template
parameters by naming, e.g. "<code>InputIterator</code>".
<p/>
There is no general specification for template parameters named "<code>Distance</code>",
as used by <code>std::advance</code> (see 24.4.3 <a href="https://wg21.link/iterator.operations">[iterator.operations]</a>).
When addressing this omission, the local restriction in 26.7.12 <a href="https://wg21.link/alg.random.sample">[alg.random.sample]</a> 
could possibly be removed.
<p/>
See the related issue <a href="lwg-defects.html#3213" title="for_each_n and copy_n missing requirements for Size (Status: Resolved)">3213</a><sup><a href="https://cplusplus.github.io/LWG/issue3213" title="Latest snapshot">(i)</a></sup> for the <code>Size</code> template parameter.
</p>

<p><i>[2020-05-09; Reflector prioritization]</i></p>

<p>
Set priority to 3 after reflector discussions.
</p>


<p id="res-3439"><b>Proposed resolution:</b></p>




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