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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __is_constructible intrinsic does not SFINAE on default member initializers"
href="https://bugs.llvm.org/show_bug.cgi?id=45158">45158</a>
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<th>Summary</th>
<td>__is_constructible intrinsic does not SFINAE on default member initializers
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>9.0
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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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>alisdairm@me.com
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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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<p>
<div>
<pre>The various standard type traits querying whether a type is constructible are
implemented (in both libc++ and libstdc++) as ultimately delegating to an
intrinsic such as __is_constructible. This trait fails to account for default
member initializers, which produce a hard error rather than returning a
true/false answer when evaluating the intrinsic, and hence the trait.
Example:
#include <type_traits>
template <class T>
struct Wrap {
Wrap() = default;
T data{}; // default member initializer
};
struct NoDefault {
NoDefault(NoDefault const&) {} // non-trivial, not an aggregate
};
int main() {
using namespace std;
static_assert(!is_default_constructible<Wrap<NoDefault>>::value, "bad");
}
Godbolt link for quick experimentation: <a href="https://godbolt.org/z/-D9mpA">https://godbolt.org/z/-D9mpA</a>
This fails with both libc++ and libstdc++, for all dialects of C++11 and later,
for all online compilers up to and including trunk.</pre>
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