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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Templated "constexpr auto" variable cannot be used for SFINAE"
href="https://bugs.llvm.org/show_bug.cgi?id=46960">46960</a>
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<th>Summary</th>
<td>Templated "constexpr auto" variable cannot be used for SFINAE
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>d25fe0be@outlook.com
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Not sure if they're the same, but it looks like that this one is related to Bug
43459 .
The following snippet compiles on Clang 8, but fails on Clang 9+ (up to trunk),
complaining "value of type 'const auto' is not implicitly convertible to
'bool'":
```cpp
#include <type_traits>
template <class T> struct C {
template <class U>
static constexpr auto constant_bool_v = sizeof(U) <= 4;
template <class U, class = std::enable_if_t<constant_bool_v<T>>>
C(U) {}
};
C<int> vvv('c');
```
Live demo: <a href="https://wandbox.org/permlink/b3r89SL8wZ8xyrzc">https://wandbox.org/permlink/b3r89SL8wZ8xyrzc</a></pre>
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