<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 1187: std::decay</title>
<meta property="og:title" content="Issue 1187: std::decay">
<meta property="og:description" content="C++ library issue. Status: C++11">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue1187.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#C++11">C++11</a> status.</em></p>
<h3 id="1187"><a href="lwg-defects.html#1187">1187</a>. <code>std::decay</code></h3>
<p><b>Section:</b> 21.3.9.7 <a href="https://wg21.link/meta.trans.other">[meta.trans.other]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Jason Merrill <b>Opened:</b> 2009-08-07 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#meta.trans.other">issues</a> in [meta.trans.other].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
I notice that <code>std::decay</code> is specified to strip the cv-quals from
anything but an array or pointer.  This seems incorrect for values of
class type, since class rvalues can have cv-qualified type (7.2.1 <a href="https://wg21.link/basic.lval">[basic.lval]</a>/9).
</p>

<p><i>[
2009-08-09 Howard adds:
]</i></p>


<blockquote><p>
See the thread starting with c++std-lib-24568 for further discussion.  And
here is a convenience link to the
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2069.html">original proposal</a>.
Also see the closely related issue <a href="lwg-defects.html#705" title="type-trait decay incompletely specified (Status: CD1)">705</a><sup><a href="https://cplusplus.github.io/LWG/issue705" title="Latest snapshot">(i)</a></sup>.
</p></blockquote>

<p><i>[
2010 Pittsburgh:  Moved to Ready.
]</i></p>




<p id="res-1187"><b>Proposed resolution:</b></p>

<p>
Add a note to <code>decay</code> in 21.3.9.7 <a href="https://wg21.link/meta.trans.other">[meta.trans.other]</a>:
</p>

<blockquote><p>
[<i>Note:</i> This behavior is similar to the lvalue-to-rvalue (4.1),
array-to-pointer (4.2), and function-to-pointer (4.3) conversions
applied when an lvalue expression is used as an rvalue, but also strips
cv-qualifiers from class types in order to more closely model by-value
argument passing. &mdash; <i>end note</i>]
</p></blockquote>








</body>
</html>
