<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 3970: &sect;[mdspan.syn] Missing definition of full_extent_t and full_extent</title>
<meta property="og:title" content="Issue 3970: &sect;[mdspan.syn] Missing definition of full_extent_t and full_extent">
<meta property="og:description" content="C++ library issue. Status: WP">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue3970.html">
<meta property="og:type" content="website">
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
<meta property="og:image:alt" content="C++ logo">
<style>
  p {text-align:justify}
  li {text-align:justify}
  pre code.backtick::before { content: "`" }
  pre code.backtick::after { content: "`" }
  blockquote.note
  {
    background-color:#E0E0E0;
    padding-left: 15px;
    padding-right: 15px;
    padding-top: 1px;
    padding-bottom: 1px;
  }
  ins {background-color:#A0FFA0}
  del {background-color:#FFA0A0}
  table.issues-index { border: 1px solid; border-collapse: collapse; }
  table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
  table.issues-index td { padding: 4px; border: 1px solid; }
  table.issues-index td:nth-child(1) { text-align: right; }
  table.issues-index td:nth-child(2) { text-align: left; }
  table.issues-index td:nth-child(3) { text-align: left; }
  table.issues-index td:nth-child(4) { text-align: left; }
  table.issues-index td:nth-child(5) { text-align: center; }
  table.issues-index td:nth-child(6) { text-align: center; }
  table.issues-index td:nth-child(7) { text-align: left; }
  table.issues-index td:nth-child(5) span.no-pr { color: red; }
  @media (prefers-color-scheme: dark) {
     html {
        color: #ddd;
        background-color: black;
     }
     ins {
        background-color: #225522
     }
     del {
        background-color: #662222
     }
     a {
        color: #6af
     }
     a:visited {
        color: #6af
     }
     blockquote.note
     {
        background-color: rgba(255, 255, 255, .10)
     }
  }
</style>
</head>
<body>
<hr>
<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#WP">WP</a> status.</em></p>
<h3 id="3970"><a href="lwg-defects.html#3970">3970</a>. &sect;[mdspan.syn] Missing definition of <code>full_extent_t</code> and <code>full_extent</code></h3>
<p><b>Section:</b> 23.7.3.2 <a href="https://wg21.link/mdspan.syn">[mdspan.syn]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> S. B. Tam <b>Opened:</b> 2023-08-16 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#mdspan.syn">issues</a> in [mdspan.syn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>submdspan</code> uses a type called <code>full_extent_t</code>, but there isn't a definition for that type.
<p/>
It appears that <code>full_extent_t</code> (along with <code>full_extent</code>) was proposed in <a href="https://wg21.link/P0009" title=" MDSPAN">P0009</a> 
before <code>submdspan</code> was moved into its own paper, and its definition failed to be included in 
<a href="https://wg21.link/P2630" title=" Submdspan">P2630</a> Submdspan.
</p>

<p><i>[2023-10-27; Reflector poll]</i></p>

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

<p><i>[2023-11-11 Approved at November 2023 meeting in Kona. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3970"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4958" title=" Working Draft, Programming Languages — C++">N4958</a>.
</p>

<ol>

<li><p>Modify 23.7.3.2 <a href="https://wg21.link/mdspan.syn">[mdspan.syn]</a> as indicated:</p>

<blockquote>
<pre>
[&hellip;]
<i>//  [mdspan.submdspan], submdspan creation</i>
template&lt;class OffsetType, class LengthType, class StrideType&gt;
  struct strided_slice;

template&lt;class LayoutMapping&gt;
  struct submdspan_mapping_result;
  
<ins>struct full_extent_t { explicit full_extent_t() = default; };
inline constexpr full_extent_t full_extent{};</ins>
[&hellip;]
</pre>
</blockquote>
</li>
</ol>





</body>
</html>
