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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - use of overloaded operator '==' is ambiguous (with reversed parameter order)"
href="https://bugs.llvm.org/show_bug.cgi?id=46508">46508</a>
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<th>Summary</th>
<td>use of overloaded operator '==' is ambiguous (with reversed parameter order)
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>10.0
</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>
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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++2a
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>dermojo@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>
<div>
<pre>Hi,
The following code is a very reduced example from a template expression
library:
class Foo {};
class X {
public:
template <typename T>
constexpr Foo operator==(const T&) const
{
return Foo{};
}
};
class A : public X {};
class B : public X {};
int main() {
Foo f = A{} == B{};
return 0;
}
It fails to compile with C++20:
<span class="quote">> clang++-10 -c sample.cpp -std=c++20</span >
sample.cpp:16:16: error: use of overloaded operator '==' is ambiguous (with
operand types 'A' and 'B')
Foo f = A{} == B{};
~~~ ^ ~~~
sample.cpp:6:18: note: candidate function [with T = B]
constexpr Foo operator==(const T&) const
^
sample.cpp:6:18: note: candidate function (with reversed parameter order)
[with T = A]
1 error generated.
I can't figure out why the reversed operator is used here (tbh, I'm not a
language lawyer).
Any help is appreciated, thanks!
<span class="quote">> clang++-10 --version</span >
clang version 10.0.0-4ubuntu1~18.04.1</pre>
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