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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Compiler is using wrong template argument when a child class calls a templated constructor of a template class."
href="https://bugs.llvm.org/show_bug.cgi?id=48365">48365</a>
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<th>Summary</th>
<td>Compiler is using wrong template argument when a child class calls a templated constructor of a template class.
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>11.0
</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>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>nicolas.brun@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<pre>The following code doesn't compile correctly:
<<
#include <type_traits>
template <typename Type>
struct CheckInt {
using success = std::bool_constant<std::is_same_v<Type, float>>;
static_assert(success());
};
template <typename T>
class Base {
public:
template <typename U, typename = typename CheckInt<U>::success>
Base(const U& v) {}
};
class Child : public Base<int> {
public:
Child() : Base(1.0f) {}
};
int main()
{
Child child; // doesn't compile
//Base<int> base(1.0f); // compiles
return 0;
}
<span class="quote">>></span >
When instantiating Child, the static_assert() fires because U evaluates to
`Base<int>` instead of `float`.
When instantiation Base<int> directly, U evaluates to `float` correctly.
The compiler generates the following error:
"
<source>:6:3: error: static_assert failed due to requirement
'std::integral_constant<bool, false>()'
static_assert(success());
^ ~~~~~~~~~
<source>:12:47: note: in instantiation of template class 'CheckInt<Base<int>>'
requested here
template <typename U, typename = typename CheckInt<U>::success>
"
The bug appears in all versions of clang (as well as gcc).
See <a href="https://godbolt.org/z/73c4Wd">https://godbolt.org/z/73c4Wd</a></pre>
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