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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - concepts: constrained member functions illegally instantiated during explicit class template instantiation"
href="https://bugs.llvm.org/show_bug.cgi?id=45204">45204</a>
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<th>Summary</th>
<td>concepts: constrained member functions illegally instantiated during explicit class template instantiation
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>10.0
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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++2a
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>akrzemi1@gmail.com
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
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<pre>The following correct C++20 program fails to compile in clang.
```
template <typename T>
concept has_a = requires(T v) { v.a(); };
template<typename T>
struct X
{
void fun(T) {}
void gun(T v) requires has_a<T> { v.a(); }
};
template struct X<int>;
```
member function `gun()` is instantiated which is a bug according to
<a href="http://eel.is/c++draft/temp.explicit#11">http://eel.is/c++draft/temp.explicit#11</a>
This works in the old experimental implementation of concepts in Clang by Saar
Raz: <a href="https://godbolt.org/z/K4SaCm">https://godbolt.org/z/K4SaCm</a></pre>
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