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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - spurious insuppressible conversion warning"
href="https://bugs.llvm.org/show_bug.cgi?id=45066">45066</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>spurious insuppressible conversion warning
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>9.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>stsp2@yandex.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>#include <iostream>
struct D;
struct B {
virtual operator D() = 0;
};
struct D : B
{
operator D() override { std::cout << "conv" << std::endl; return D(); }
};
.
int main()
{
D obj;
B& br = obj;
(D)br; // calls D::operator D() through virtual dispatch
return 0;
}
$ clang++ -Wall -o vconv vconv.cpp
vconv.cpp:9:5: warning: conversion function converting 'D' to itself will never
be used
operator D() override { std::cout << "conv" << std::endl; return D(); }
^
1 warning generated.
$ ./vconv
conv
The example above shows that the warning
is spurious. Converting to the same type
will indeed never use the conversion
operator. But the above case converts
from B to D, so the warning does not apply.
It may be quite difficult to check properly,
but in this particular example the "override"
keyword is a clear hint that it is going
to be used via the virtual dispatch.
Note that with gcc it is at least possible
to suppress that warning with -Wno-class-conversion.
But in clang it is persistent.</pre>
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