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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 - Compound requirement type constraint uses decltype(E) instead of decltype((E))"
href="https://bugs.llvm.org/show_bug.cgi?id=45088">45088</a>
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<th>Summary</th>
<td>Compound requirement type constraint uses decltype(E) instead of decltype((E))
</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
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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>kjcamann.lists@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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<pre>The following program should compile in clang but does not. It does work in gcc
10:
```
#include <type_traits>
template <typename T>
concept reference = std::is_reference_v<T>;
struct S {
int i;
};
template <typename T>
concept C = requires(T &t) {
{ t.i } -> reference;
};
static_assert( C<S> ); // static_assert fails
```
The issue here is that according to [expr.prim.req.compound]p1.3.2, the type
substituted into the type constraint should be decltype((E)), with the extra
parentheses to inhibit the corner case rule for decltype
([dcl.type.decltype]p1.3) that makes id expressions and class member access
expressions into just T rather than the normal T& for lvalue category
expressions. clang uses `decltype(E)` rather than `decltype((E))` and even says
so in the diagnostic:
"note: because 'decltype(t.i)' (aka 'int') does not satisfy 'reference'"
This bug is present in both clang 10 and in trunk.</pre>
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