<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 2990: optional::value_type is not always a value type</title>
<meta property="og:title" content="Issue 2990: optional::value_type is not always a value type">
<meta property="og:description" content="C++ library issue. Status: Open">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue2990.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#Open">Open</a> status.</em></p>
<h3 id="2990"><a href="lwg-active.html#2990">2990</a>. <code>optional::value_type</code> is not always a value type</h3>
<p><b>Section:</b> 22.5.3 <a href="https://wg21.link/optional.optional">[optional.optional]</a> <b>Status:</b> <a href="lwg-active.html#Open">Open</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2017-06-27 <b>Last modified:</b> 2018-01-28</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#optional.optional">issues</a> in [optional.optional].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Open">Open</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>optional&lt;T&gt;::value_type</code> is <code>T</code>, which can be a <i>cv</i>-qualified object type. This is 
inconsistent with the uses of the name <code>value_type</code> elsewhere in the standard. We should either require 
<code>optional&lt;T&gt;::value_type</code> to be <code>remove_cv_t&lt;T&gt;</code> &mdash; a true value type &mdash; 
or rename the type alias to <code>element_type</code>.
</p>

<p><i>[2017-07 Toronto Tuesday PM issue prioritization]</i></p>

<p>Priority 3; may also affect <code>array</code></p>

<p><i>[2018-1-26 issues processing telecon]</i></p>

<p>Status to 'Open'</p>


<p id="res-2990"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4659">N4659</a>.
</p>

<ol>
<li><p>Edit 22.5.3 <a href="https://wg21.link/optional.optional">[optional.optional]</a>, class template <code>optional</code> synopsis, as indicated:</p>

<blockquote>
<pre>
template &lt;class T&gt;
  class optional {
  public:
    using value_type = <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins>;
    [&hellip;]
  };
</pre>
</blockquote>
</li>
</ol>




</body>
</html>
