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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 - Bogus "reference to local variable error" with lambda in fold expression over comma and assignment"
href="https://bugs.llvm.org/show_bug.cgi?id=41576">41576</a>
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<th>Summary</th>
<td>Bogus "reference to local variable error" with lambda in fold expression over comma and assignment
</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
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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++'17
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>vittorio.romeo@outlook.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>The following code
#include <tuple>
template <class T>
struct X
{
template <class F>
void f(F f)
{
f(0);
}
};
template <class... Xs>
void bug(X<Xs>... xs)
{
std::tuple<Xs...> t;
std::apply([&](auto&... ys)
{
(xs.f([&](auto y)
{
ys = y;
}), ...);
}, t);
}
int main()
{
bug(X<int>{});
}
produces a bogus error with clang++ (version 9.0.0 (trunk 359058))
<source>:20:10: error: reference to local variable 'xs' declared in
enclosing function 'bug<int>'
(xs.f([&](auto y)
^
The bug can be reproduced on godbolt.org here:
<a href="https://gcc.godbolt.org/z/NNLI5p">https://gcc.godbolt.org/z/NNLI5p</a>
---
Changing the lambda to the following
std::apply([&xs...](auto&... ys)
{
(xs.f([&ys...](auto y)
{
ys = y;
}), ...);
}, t);
fixes the error:
<a href="https://gcc.godbolt.org/z/hp2hMN">https://gcc.godbolt.org/z/hp2hMN</a></pre>
</div>
</p>
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