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<title>Issue 440: Should std::complex use unqualified transcendentals?</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#NAD">NAD</a> status.</em></p>
<h3 id="440"><a href="lwg-closed.html#440">440</a>. Should std::complex use unqualified transcendentals?</h3>
<p><b>Section:</b> 29.4.8 <a href="https://wg21.link/complex.transcendentals">[complex.transcendentals]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Matt Austern <b>Opened:</b> 2003-11-05 <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#complex.transcendentals">issues</a> in [complex.transcendentals].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Operations like <code>pow</code> and <code>exp</code> on
<code>complex&lt;T&gt;</code> are typically implemented in terms of
operations like <code>sin</code> and <code>cos</code> on <code>T</code>.  
Should implementations write this as <code>std::sin</code>, or as plain
unqualified <code>sin</code>?
</p>

<p>The issue, of course, is whether we want to use
argument-dependent lookup in the case where <code>T</code> is a
user-defined type.  This is similar to the issue of valarray
transcendentals, as discussed in issue <a href="lwg-defects.html#226" title="User supplied specializations or overloads of namespace std function templates (Status: CD1)">226</a><sup><a href="https://cplusplus.github.io/LWG/issue226" title="Latest snapshot">(i)</a></sup>.</p>

<p>This issue differs from valarray transcendentals in two important
ways.  First, "the effect of instantiating the template
<code>complex</code> for types other than float, double or long double is
unspecified." (29.4.2 <a href="https://wg21.link/complex.syn">[complex.syn]</a>) Second, the standard does not
dictate implementation, so there is no guarantee that a particular
real math function is used in the implementation of a particular
complex function.</p>



<p id="res-440"><b>Proposed resolution:</b></p>


<p><b>Rationale:</b></p>
<p>If you instantiate std::complex for user-defined types, all bets
are off.</p>





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