<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 559: numeric_limits&lt;const T&gt;</title>
<meta property="og:title" content="Issue 559: numeric_limits&lt;const T&gt;">
<meta property="og:description" content="C++ library issue. Status: CD1">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue559.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#CD1">CD1</a> status.</em></p>
<h3 id="559"><a href="lwg-defects.html#559">559</a>. numeric_limits&lt;const T&gt;</h3>
<p><b>Section:</b> 17.3.5 <a href="https://wg21.link/numeric.limits">[numeric.limits]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2006-02-19 <b>Last modified:</b> 2017-06-15</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#numeric.limits">active issues</a> in [numeric.limits].</p>
<p><b>View all other</b> <a href="lwg-index.html#numeric.limits">issues</a> in [numeric.limits].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
        <p>

 [limits], p2 requires implementations  to provide specializations of the
<code>numeric_limits</code> template for  each scalar type. While this
could be interepreted to include cv-qualified forms of such types such
an  interepretation   is  not  reflected   in  the  synopsis   of  the
<code>&lt;limits&gt;</code> header.

        </p>
        <p>

The absence  of specializations of the template  on cv-qualified forms
of  fundamental types  makes <code>numeric_limits</code>  difficult to
use in generic  code where the constness (or volatility)  of a type is
not  always  immediately  apparent.  In  such  contexts,  the  primary
template  ends   up  being   instantiated  instead  of   the  provided
specialization, typically yielding unexpected behavior.

        </p>
        <p>

Require   that  specializations   of   <code>numeric_limits</code>  on
cv-qualified fundamental types have the same semantics as those on the
unqualifed forms of the same types.

        </p>


<p id="res-559"><b>Proposed resolution:</b></p>
        <p>

Add  to  the   synopsis  of  the  <code>&lt;limits&gt;</code>  header,
immediately  below  the  declaration  of  the  primary  template,  the
following:
</p>

<pre>

template &lt;class T&gt; class numeric_limits&lt;const T&gt;;
template &lt;class T&gt; class numeric_limits&lt;volatile T&gt;;
template &lt;class T&gt; class numeric_limits&lt;const volatile T&gt;;

</pre>

        <p>

Add  a new paragraph  to the  end of  17.3.5 <a href="https://wg21.link/numeric.limits">[numeric.limits]</a>, with  the following
text:

        </p>
        <p>

-new-para- The  value of each member  of a <code>numeric_limits</code>
specialization on a  cv-qualified T is equal to the  value of the same
member of <code>numeric_limits&lt;T&gt;</code>.

        </p>

<p><i>[
Portland: Martin will clarify that user-defined types get cv-specializations
automatically.
]</i></p>







</body>
</html>
