<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 869: Bucket (local) iterators and iterating past end</title>
<meta property="og:title" content="Issue 869: Bucket (local) iterators and iterating past end">
<meta property="og:description" content="C++ library issue. Status: C++11">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue869.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="869"><a href="lwg-defects.html#869">869</a>. Bucket (local) iterators and iterating past end</h3>
<p><b>Section:</b> 23.2.8 <a href="https://wg21.link/unord.req">[unord.req]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Sohail Somani <b>Opened:</b> 2008-07-22 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#unord.req">active issues</a> in [unord.req].</p>
<p><b>View all other</b> <a href="lwg-index.html#unord.req">issues</a> in [unord.req].</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>
Is there any language in the current draft specifying the behaviour of the following snippet?
</p>

<blockquote><pre>
unordered_set&lt;int&gt; s;
unordered_set&lt;int&gt;::local_iterator it = s.end(0);

// Iterate past end - the unspecified part
it++;
</pre></blockquote>

<p>
I don't think there is anything about <code>s.end(n)</code> being considered an
iterator for the past-the-end value though (I think) it should be.
</p>

<p><i>[
San Francisco:
]</i></p>


<blockquote><p>
We believe that this is not a substantive change, but the proposed
change to the wording is clearer than what we have now.
</p></blockquote>

<p><i>[
Post Summit:
]</i></p>


<blockquote><p>
Recommend Tentatively Ready.
</p></blockquote>



<p id="res-869"><b>Proposed resolution:</b></p>
<p>
Change Table 97 "Unordered associative container requirements" in 23.2.8 <a href="https://wg21.link/unord.req">[unord.req]</a>:
</p>

<blockquote>
<table border="1">
<caption>Table 97: Unordered associative container requirements</caption>
<tr>
<th>expression</th><th>return type</th><th>assertion&#47;note pre&#47;post-condition</th><th>complexity</th>
</tr>
<tr>
<td><code>b.begin(n)</code></td>
<td><code>local_iterator</code><br/><code>const_local_iterator</code> for const <code>b</code>.</td>
<td>Pre: n shall be in the range [0,b.bucket_count()). <del>Note: [b.begin(n), b.end(n)) is a
valid range containing all of the elements in the n<sup>th</sup> bucket.</del>
<ins><code>b.begin(n)</code> returns an iterator referring to the first element in the bucket.
If the bucket is empty, then <code>b.begin(n) == b.end(n)</code>.</ins></td>
<td>Constant</td>
</tr>
<tr>
<td><code>b.end(n)</code></td>
<td><code>local_iterator</code><br/><code>const_local_iterator</code> for const <code>b</code>.</td>
<td>Pre: n shall be in the range <code>[0, b.bucket_count())</code>.
<ins><code>b.end(n)</code> returns an iterator which is the past-the-end value for the bucket.</ins></td>
<td>Constant</td>
</tr>
</table>
</blockquote>






</body>
</html>
