<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 2375: Is [iterator.requirements.general]/9 too broadly applied?</title>
<meta property="og:title" content="Issue 2375: Is [iterator.requirements.general]/9 too broadly applied?">
<meta property="og:description" content="C++ library issue. Status: Resolved">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue2375.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="2375"><a href="lwg-defects.html#2375">2375</a>. Is [iterator.requirements.general]/9 too broadly applied?</h3>
<p><b>Section:</b> 24.3.1 <a href="https://wg21.link/iterator.requirements.general">[iterator.requirements.general]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Marshall Clow <b>Opened:</b> 2014-03-25 <b>Last modified:</b> 2021-06-23</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#iterator.requirements.general">issues</a> in [iterator.requirements.general].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
24.3.1 <a href="https://wg21.link/iterator.requirements.general">[iterator.requirements.general]</a> p9 says:
</p>
<blockquote><p>
Destruction of an iterator may invalidate pointers and references previously obtained from that iterator.
</p></blockquote>
<p>
But the resolution of LWG issue <a href="lwg-defects.html#2360" title="reverse_iterator::operator*() is unimplementable (Status: C++14)">2360</a><sup><a href="https://cplusplus.github.io/LWG/issue2360" title="Latest snapshot">(i)</a></sup> specifically advocates returning <code>*--temp;</code> where <code>temp</code> is a 
local variable.
<p/>
And 24.3.5.5 <a href="https://wg21.link/forward.iterators">[forward.iterators]</a> p6 says:
</p>
<blockquote><p>
If <code>a</code> and <code>b</code> are both dereferenceable, then <code>a == b</code> if and only if <code>*a</code> and <code>*b</code> are bound 
to the same object.
</p></blockquote>
<p>
which disallows "stashing" iterators (i.e, iterators that refer to data inside themselves).
<p/>
So, I suspect that the restriction in p9 should only apply to input iterators, and can probably be moved into 
24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a> instead of 24.3.1 <a href="https://wg21.link/iterator.requirements.general">[iterator.requirements.general]</a>.
</p>

<p><i>[2014-05-22, Daniel comments]</i></p>


<p>
Given that forward iterators (and beyond) are refinements of input iterator, moving this constraint to input iterators won't help
much because it would still hold for all refined forms. 
</p>

<p><i>[2021-06-23 Resolved by adoption of <a href="https://wg21.link/P0896R4" title=" The One Ranges Proposal">P0896R4</a> in San Diego. Status changed: New &rarr; Resolved.]</i></p>



<p id="res-2375"><b>Proposed resolution:</b></p>





</body>
</html>
