<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 2693: constexpr for various std::complex arithmetic and value operators</title>
<meta property="og:title" content="Issue 2693: constexpr for various std::complex arithmetic and value operators">
<meta property="og:description" content="C++ library issue. Status: Resolved">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue2693.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#Resolved">Resolved</a> status.</em></p>
<h3 id="2693"><a href="lwg-defects.html#2693">2693</a>. <code>constexpr</code> for various <code>std::complex</code> arithmetic and value operators</h3>
<p><b>Section:</b> 29.4 <a href="https://wg21.link/complex.numbers">[complex.numbers]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Oliver Rosten <b>Opened:</b> 2016-04-14 <b>Last modified:</b> 2018-06-12</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#complex.numbers">issues</a> in [complex.numbers].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
This modification will allow complex-number arithmetic to be performed at compile time. From a mathematical 
standpoint, it is natural (and desirable) to treat complex numbers on the same footing as the reals. 
From a programming perspective, this change will broaden the scope in which <code>std::complex</code> can be used, 
allowing it to be smoothly incorporated into classes exploiting <code>constexpr</code>.
<p/>
Suggested resolution:
<p/>
The following functions in the <code>std::complex</code> namespace should be made <code>constexpr</code>:
</p>
<ol>
<li><p>
Section 29.4.5 <a href="https://wg21.link/complex.member.ops">[complex.member.ops]</a>: The member (arithmetic) operators 
{<code>+=</code>, <code>-=</code>, <code>/=</code>, <code>*=</code>}
</p></li>
<li><p>
Section 29.4.6 <a href="https://wg21.link/complex.ops">[complex.ops]</a>: The arithmetic operators unary operators {<code>+</code>, <code>-</code>} 
and binary operators {<code>+</code>, <code>-</code>, <code>/</code>, <code>*</code>};
</p></li>
<li><p>
Section 29.4.7 <a href="https://wg21.link/complex.value.ops">[complex.value.ops]</a>: The 'value' operators <code>abs</code>, <code>norm</code>, and <code>conj</code>.
</p></li>
</ol>
<p>
In terms of modification of the standard, all that is required is the insertion of the <code>constexpr</code> specifier 
in the relevant parts of:
</p>
<ol>
<li><p>
Section 29.4.2 <a href="https://wg21.link/complex.syn">[complex.syn]</a> (the Header synopsis), together with the corresponding entries in sections 
29.4.6 <a href="https://wg21.link/complex.ops">[complex.ops]</a> and 29.4.7 <a href="https://wg21.link/complex.value.ops">[complex.value.ops]</a>.
</p></li>
<li><p>
Sections 29.4.3 <a href="https://wg21.link/complex">[complex]</a>,  [complex.special] (class template and specializations), together 
with the corresponding entries in section 29.4.5 <a href="https://wg21.link/complex.member.ops">[complex.member.ops]</a>.
</p></li>
</ol>

<p><i>[2016-05 Issues Telecon]</i></p>

<p>
This kind of work (new feature) has been being done via papers rather than via the issues list.
</p>
<p>
Walter believes that he knows someone who would be willing to write such a paper.
</p>

<p><i>[2018-06 Rapperswil Wednesday issues processing]</i></p>

<p>This was resolved by <a href="https://wg21.link/P0415">P0415</a>, which was adopted in Albequerque.</p>


<p id="res-2693"><b>Proposed resolution:</b></p>





</body>
</html>
