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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - decltype resolution ignores SFINAE"
href="https://bugs.llvm.org/show_bug.cgi?id=40989">40989</a>
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<th>Summary</th>
<td>decltype resolution ignores SFINAE
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</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>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++11
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>Simon.Richter@hogyros.de
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<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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<pre>GCC exhibits the same bug, see
<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89564">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89564</a>
This is related, but not identical to #40988.
I'm trying to build a commutative operator+ for a class, as a freestanding
template operator+ that accepts my class on the right hand side and reverses
the argument order:
#include <type_traits>
struct one {};
struct two
{
two() { }
two(one const &) { }
operator one() const { return one{}; }
};
template<typename T>
auto operator+(T const &lhs, two const &rhs) -> typename
std::enable_if<!std::is_same<T, two>::value, decltype(rhs + lhs)>::type
{
return rhs + lhs;
}
void test()
{
one o;
two t;
auto a = o + t;
}
This code should have been rejected, because no usable operator+ exists for the
expression "rhs + lhs". Instead, the template is specialized recursively trying
to resolve the decltype.
icc and MSVC correctly reject this code with the expected diagnostic.</pre>
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