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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Static value in depended class is treated as non-constant expression."
href="https://bugs.llvm.org/show_bug.cgi?id=33089">33089</a>
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<th>Summary</th>
<td>Static value in depended class is treated as non-constant expression.
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.9
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++11
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>tomaszkam@gmail.com
</td>
</tr>
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>For following code:
#include <type_traits>
template<typename U, typename T>
decltype(U{T::value}) foo(T, int) { return T::value; }
template<typename U, typename T>
U foo(T, ...) = delete;
int main()
{
foo<short>(std::integral_constant<int, 20>{}, 0);
}
Candidate foo(T, int) is ignored with following error:
substitution failure [with U = short, T = std::__1::integral_constant<int,
20>]: non-constant-expression cannot be narrowed from type 'int' to 'short' in
initializer list decltype(U{T::value}) foo(T, int) { return T::value; }
As suggested the T::value is not constexpr expression, despite declared as
constexpr.
If the declaration is changed to us an compile time conversion operator, the
expression is properly regonized as compile time constant, and brace
initialization is well-formed.
template<typename U, typename T>
decltype(U{T{}}) foo(T, int) { return T::value; }</pre>
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