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<title>Issue 1229: error_code operator= typo</title>
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<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="1229"><a href="lwg-defects.html#1229">1229</a>. <code>error_code operator=</code> typo</h3>
<p><b>Section:</b> 19.5.4.3 <a href="https://wg21.link/syserr.errcode.modifiers">[syserr.errcode.modifiers]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2009-10-08 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2960.pdf">N2960</a>
19.5.4.1 <a href="https://wg21.link/syserr.errcode.overview">[syserr.errcode.overview]</a> and 19.5.4.3 <a href="https://wg21.link/syserr.errcode.modifiers">[syserr.errcode.modifiers]</a> say:
</p>

<blockquote><pre> 
template &lt;class ErrorCodeEnum&gt;
  typename enable_if&lt;is_error_code_enum&lt;ErrorCodeEnum&gt;::value&gt;::type&amp;
    operator=(ErrorCodeEnum e);
</pre></blockquote>

<p>
They should say:
</p>

<blockquote><pre> 
template &lt;class ErrorCodeEnum&gt;
  typename enable_if&lt;is_error_code_enum&lt;ErrorCodeEnum&gt;::value, error_code&gt;::type&amp;
    operator=(ErrorCodeEnum e);
</pre></blockquote>

<p>
Or (I prefer this form):
</p>
 
<blockquote><pre> 
template &lt;class ErrorCodeEnum&gt;
  typename enable_if&lt;is_error_code_enum&lt;ErrorCodeEnum&gt;::value, error_code&amp;&gt;::type
    operator=(ErrorCodeEnum e);
</pre></blockquote>

<p>
This is because <code>enable_if</code> is declared as (21.3.9.7 <a href="https://wg21.link/meta.trans.other">[meta.trans.other]</a>):
</p>
 
<blockquote><pre> 
template &lt;bool B, class T = void&gt; struct enable_if;
</pre></blockquote>

<p>
So, the current wording makes <code>operator=</code> return
<code>void&amp;</code>, which is not good.
</p>

<p> 
19.5.4.3 <a href="https://wg21.link/syserr.errcode.modifiers">[syserr.errcode.modifiers]</a>/4 says
</p>

<blockquote><p>
<i>Returns:</i> <code>*this</code>.
</p></blockquote>
<p>
which is correct.
</p>

<p>
Additionally,
</p>

<p>
19.5.5.1 <a href="https://wg21.link/syserr.errcondition.overview">[syserr.errcondition.overview]</a>/1 says:
</p>
 
<blockquote><pre> 
template&lt;typename ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;, error_code&gt;::type &amp;
    operator=( ErrorConditionEnum e );
</pre></blockquote>

<p>
Which contains several problems (<code>typename</code> versus <code>class</code>
inconsistency, lack of <code>::value</code>, <code>error_code</code> instead of
<code>error_condition</code>), while 19.5.5.3 <a href="https://wg21.link/syserr.errcondition.modifiers">[syserr.errcondition.modifiers]</a> says:
</p>
 
<blockquote><pre> 
template &lt;class ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;::value&gt;::type&amp;
    operator=(ErrorConditionEnum e);
</pre></blockquote>

<p>
Which returns <code>void&amp;</code>.  They should both say:
</p>
 
<blockquote><pre> 
template &lt;class ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;::value, 
  error_condition&gt;::type&amp;
    operator=(ErrorConditionEnum e);
</pre></blockquote>

<p>
Or (again, I prefer this form):
</p>

<blockquote><pre> 
template &lt;class ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;::value, 
  error_condition&amp;&gt;::type
    operator=(ErrorConditionEnum e);
</pre></blockquote>

<p>
Additionally, 19.5.5.3 <a href="https://wg21.link/syserr.errcondition.modifiers">[syserr.errcondition.modifiers]</a> lacks a
"<i>Returns:</i> <code>*this</code>." paragraph, which is presumably
necessary.
</p>

<p><i>[
2009-10-18 Beman adds:
]</i></p>


<blockquote><p>
The proposed resolution for issue <a href="lwg-defects.html#1237" title="Constrained error_code&#47;error_condition members (Status: C++11)">1237</a><sup><a href="https://cplusplus.github.io/LWG/issue1237" title="Latest snapshot">(i)</a></sup> makes this issue
moot, so it should become NAD.
</p></blockquote>

<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
<del>NAD</del><ins>Resolved</ins>, solved by <a href="lwg-defects.html#1237" title="Constrained error_code&#47;error_condition members (Status: C++11)">1237</a><sup><a href="https://cplusplus.github.io/LWG/issue1237" title="Latest snapshot">(i)</a></sup>.
</p></blockquote>



<p id="res-1229"><b>Proposed resolution:</b></p>

<p>
Change 19.5.4.1 <a href="https://wg21.link/syserr.errcode.overview">[syserr.errcode.overview]</a> and 19.5.4.3 <a href="https://wg21.link/syserr.errcode.modifiers">[syserr.errcode.modifiers]</a>:
</p>

<blockquote><pre>
template &lt;class ErrorCodeEnum&gt;
  typename enable_if&lt;is_error_code_enum&lt;ErrorCodeEnum&gt;::value<ins>, 
  error_code&amp;</ins>&gt;::type<del>&amp;</del>
    operator=(ErrorCodeEnum e);
</pre></blockquote>

<p>
Change 19.5.5.1 <a href="https://wg21.link/syserr.errcondition.overview">[syserr.errcondition.overview]</a>:
</p>

<blockquote><pre>
template&lt;<del>typename</del> <ins>class</ins> ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;<ins>::value</ins>, 
  error_co<ins>ndition</ins><del>de</del><ins>&amp;</ins>&gt;::type<del> &amp;</del>
    operator=( ErrorConditionEnum e );
</pre></blockquote>

<p>
Change 19.5.5.3 <a href="https://wg21.link/syserr.errcondition.modifiers">[syserr.errcondition.modifiers]</a>:
</p>

<blockquote><pre>
template &lt;class ErrorConditionEnum&gt;
  typename enable_if&lt;is_error_condition_enum&lt;ErrorConditionEnum&gt;::value<ins>, 
  error_condition&amp;</ins>&gt;::type<del>&amp;</del>
    operator=(ErrorConditionEnum e);
</pre>
<blockquote>
<p>
<i>Postcondition:</i> <code>*this == make_error_condition(e)</code>.
</p>
<p><ins>
<i>Returns:</i> <code>*this</code>.
</ins></p>
<p>
<i>Throws:</i> Nothing.
</p>
</blockquote>
</blockquote>






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