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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - std::complex with a custom type does not work because of how std::__promote is defined"
href="https://llvm.org/bugs/show_bug.cgi?id=30589">30589</a>
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<th>Summary</th>
<td>std::complex with a custom type does not work because of how std::__promote is defined
</td>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>hfinkel@anl.gov
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=17394" name="attach_17394" title="test case">attachment 17394</a> <a href="attachment.cgi?id=17394&action=edit" title="test case">[details]</a></span>
test case
In <a href="https://reviews.llvm.org/D18639">https://reviews.llvm.org/D18639</a>, Eric asked if we supporting using
std::complex with custom numeric types. The answer is: mostly. I've attached
the test case I started writing. This compiles with libstdc++, and in fact,
requires a lot less of the custom type than we do (e.g. we require fabs in
addition to abs, scalbn, logb, and many other functions). With libc++, however,
we do it one compilation error which looks like a problem with libc++ itself:
include/c++/v1/complex:1321:39: error: no matching function for call to 'pow'
complex<_Tp> __z = log(__x + sqrt(pow(__x, _Tp(2)) - _Tp(1)));
...
include/c++/v1/complex:1109:1: note: candidate template ignored: substitution
failure [with _Tp = ct::va
lue, _Up = ct::value]: no type named 'type' in 'std::__1::__promote<ct::value,
ct::value, void>'
pow(const complex<_Tp>& __x, const _Up& __y)
The problem here seems to be that std::__promote, which is defined in
type_traits, only works for types for which __numeric_type<T>::type exists, and
that is only for builtin numeric types. As a result, this template does not
match:
template<class _Tp, class _Up>
inline _LIBCPP_INLINE_VISIBILITY
typename enable_if
<
is_arithmetic<_Up>::value,
complex<typename __promote<_Tp, _Up>::type>
<span class="quote">>::type</span >
pow(const complex<_Tp>& __x, const _Up& __y)
{
typedef complex<typename __promote<_Tp, _Up>::type> result_type;
return _VSTD::pow(result_type(__x), result_type(__y));
}</pre>
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