<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 3445: [networking.ts] net::basic_socket_istream::connect should be constrained</title>
<meta property="og:title" content="Issue 3445: [networking.ts] net::basic_socket_istream::connect should be constrained">
<meta property="og:description" content="C++ library issue. Status: LEWG">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue3445.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#LEWG">LEWG</a> status.</em></p>
<h3 id="3445"><a href="lwg-active.html#3445">3445</a>. [networking.ts] <code>net::basic_socket_istream::connect</code> should be constrained</h3>
<p><b>Section:</b> 19.2.1 [networking.ts::socket.iostream.cons], 19.2.2 [networking.ts::socket.iostream.members] <b>Status:</b> <a href="lwg-active.html#LEWG">LEWG</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2020-05-14 <b>Last modified:</b> 2021-05-10</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#networking.ts::socket.iostream.cons">issues</a> in [networking.ts::socket.iostream.cons].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#LEWG">LEWG</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: networking.ts</b></p>
<p>
<code>basic_socket_streambuf&lt;P, C, W&gt;::connect(Args&amp;&amp;...)</code> is constrained to only exist when 
<code>P</code> meets the <code>InternetProtocol</code> requirements, but <code>basic_socket_iostream&lt;P, C, W&gt;::connect(Args&amp;&amp;...)</code> 
is not constrained. Since it just passes those arguments straight to the <code>streambuf</code>, the outer 
<code>connect(Args&amp;&amp;...)</code> should be constrained too.
<p/>
In addition to that, the <code>basic_socket_iostream(Args&amp;&amp;...)</code> constructor should be constrained, so that 
<code>is_constructible</code> gives the right answer.
</p>

<p><i>[2020-07-17; Priority set to 3 in telecon]</i></p>



<p id="res-3445"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4771">N4771</a>.</p>

<ol>
<li><p>Modify 19.2.1 [networking.ts::socket.iostream.cons] as indicated:</p>

<blockquote class="note">
<p>
[<i>Drafting note:</i> As a drive-by fix, a missing <code>std::</code> qualification in front of <code>forward</code> has been added]
</p>
</blockquote>

<blockquote>
<pre>
template&lt;class... Args&gt;
  explicit basic_socket_iostream(Args&amp;&amp;... args);
</pre>
<blockquote>
<p>
-4- <i>Effects:</i> Initializes the base class as <code>basic_iostream&lt;char&gt;(&amp;sb_))</code>, 
value-initializes <code>sb_</code>, and performs <code>setf(std::ios_base::unitbuf)</code>. Then calls 
<code>rdbuf()-&gt;connect(<ins>std::</ins>forward&lt;Args&gt;(args)...)</code>. If that function returns a null pointer, 
calls <code>setstate(failbit)</code>.
<p/>
<ins>-?- <i>Remarks:</i> This function shall not participate in overload resolution unless the expression 
<code>rdbuf()-&gt;connect(std::forward&lt;Args&gt;(args)...)</code> is well-formed.</ins>
</p>
</blockquote>
</blockquote>
</li>

<li><p>Modify 19.2.2 [networking.ts::socket.iostream.members] as indicated:</p>

<blockquote class="note">
<p>
[<i>Drafting note:</i> As a drive-by fix, a missing <code>std::</code> qualification in front of <code>forward</code> has been added]
</p>
</blockquote>

<blockquote>
<pre>
template&lt;class... Args&gt;
  void connect(Args&amp;&amp;... args);
</pre>
<blockquote>
<p>
-1- <i>Effects:</i> Calls <code>rdbuf()-&gt;connect(<ins>std::</ins>forward&lt;Args&gt;(args)...)</code>. If that function 
returns a null pointer, calls <code>setstate(failbit)</code> (which may throw <code>ios_base::failure</code>).
<p/>
<ins>-?- <i>Remarks:</i> This function shall not participate in overload resolution unless the expression 
<code>rdbuf()-&gt;connect(std::forward&lt;Args&gt;(args)...)</code> is well-formed.</ins>
</p>
</blockquote>
</blockquote>
</li>

</ol>




</body>
</html>
