<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 674: shared_ptr interface changes for consistency with N1856</title>
<meta property="og:title" content="Issue 674: shared_ptr interface changes for consistency with N1856">
<meta property="og:description" content="C++ library issue. Status: CD1">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue674.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="674"><a href="lwg-defects.html#674">674</a>. <code>shared_ptr</code> interface changes for consistency with N1856</h3>
<p><b>Section:</b> 20.3.2.2 <a href="https://wg21.link/util.smartptr.shared">[util.smartptr.shared]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2007-05-05 <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#util.smartptr.shared">issues</a> in [util.smartptr.shared].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1856.html">N1856</a> does not propose
any changes to <code>shared_ptr</code>. It needs to be updated to use a rvalue reference where appropriate
and to interoperate with <code>unique_ptr</code> as it does with <code>auto_ptr</code>.
</p>


<p id="res-674"><b>Proposed resolution:</b></p>

<p>
Change 20.3.2.2 <a href="https://wg21.link/util.smartptr.shared">[util.smartptr.shared]</a> as follows:
</p>

<blockquote>
<pre>template&lt;class Y&gt; explicit shared_ptr(auto_ptr&lt;Y&gt;<del>&amp;</del><ins>&amp;&amp;</ins> r);
<ins>template&lt;class Y, class D&gt; explicit shared_ptr(const unique_ptr&lt;Y,D&gt;&amp; r) = delete;
template&lt;class Y, class D&gt; explicit shared_ptr(unique_ptr&lt;Y,D&gt;&amp;&amp; r);</ins>
...
template&lt;class Y&gt; shared_ptr&amp; operator=(auto_ptr&lt;Y&gt;<del>&amp;</del><ins>&amp;&amp;</ins> r);
<ins>template&lt;class Y, class D&gt; shared_ptr&amp; operator=(const unique_ptr&lt;Y,D&gt;&amp; r) = delete;
template&lt;class Y, class D&gt; shared_ptr&amp; operator=(unique_ptr&lt;Y,D&gt;&amp;&amp; r);</ins></pre>
</blockquote>

<p>
Change 20.3.2.2.2 <a href="https://wg21.link/util.smartptr.shared.const">[util.smartptr.shared.const]</a> as follows:
</p>

<blockquote>
<pre><ins>template&lt;class Y&gt; shared_ptr(auto_ptr&lt;Y&gt;<del>&amp;</del><ins>&amp;&amp;</ins> r);</ins></pre>
</blockquote>

<p>
Add to 20.3.2.2.2 <a href="https://wg21.link/util.smartptr.shared.const">[util.smartptr.shared.const]</a>:
</p>

<blockquote>
<pre><ins>template&lt;class Y, class D&gt; shared_ptr(unique_ptr&lt;Y, D&gt;&amp;&amp; r);</ins></pre>
<blockquote>

<p><ins>
<i>Effects:</i> Equivalent to <code>shared_ptr( r.release(), r.get_deleter() )</code> when <code>D</code> is
          not a reference type, <code>shared_ptr( r.release(), ref( r.get_deleter() ) )</code>
          otherwise.
</ins></p>

<p><ins>
<i>Exception safety:</i> If an exception is thrown, the constructor has no effect.
</ins></p>
</blockquote>

</blockquote>

<p>
Change 20.3.2.2.4 <a href="https://wg21.link/util.smartptr.shared.assign">[util.smartptr.shared.assign]</a> as follows:
</p>

<blockquote>
<pre>template&lt;class Y&gt; shared_ptr&amp; operator=(auto_ptr&lt;Y&gt;<del>&amp;</del><ins>&amp;&amp;</ins> r);</pre>
</blockquote>

<p>
Add to 20.3.2.2.4 <a href="https://wg21.link/util.smartptr.shared.assign">[util.smartptr.shared.assign]</a>:
</p>

<blockquote>
<pre><ins>template&lt;class Y, class D&gt; shared_ptr&amp; operator=(unique_ptr&lt;Y,D&gt;&amp;&amp; r);</ins></pre>

<blockquote>
<p><ins>
-4- <i>Effects:</i> Equivalent to <code>shared_ptr(std::move(r)).swap(*this)</code>.
</ins></p>
<p><ins>
-5- <i>Returns:</i> <code>*this</code>.
</ins></p>
</blockquote>

</blockquote>



<p><i>[
Kona (2007): We may need to open an issue (<a href="lwg-defects.html#743" title="rvalue swap for shared_ptr (Status: CD1)">743</a><sup><a href="https://cplusplus.github.io/LWG/issue743" title="Latest snapshot">(i)</a></sup>) to deal with the question of
whether <code>shared_ptr</code> needs an rvalue <code>swap</code>.
]</i></p>





</body>
</html>
