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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - A conversion function template shall not have a deduced return type"
href="https://bugs.llvm.org/show_bug.cgi?id=52434">52434</a>
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<th>Summary</th>
<td>A conversion function template shall not have a deduced return type
</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>Windows NT
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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
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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>fchelnokov@gmail.com
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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>
<div>
<pre>This code is invalid:
```
struct S {
template<class=void>
operator auto() const { return 2; }
};
int main() {
S s;
[[maybe_unused]] int d = s;
}
```
because the standard explicitly prohibits conversion function template having a
deduced return type:
<a href="https://timsong-cpp.github.io/cppwp/n4861/class.conv.fct#6">https://timsong-cpp.github.io/cppwp/n4861/class.conv.fct#6</a>
But now Clang accepts the program:
<a href="https://gcc.godbolt.org/z/rMK4zboEd">https://gcc.godbolt.org/z/rMK4zboEd</a>
which is a bug.</pre>
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