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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Trivial type with defaulted assignment and destructor is not usable in constexpr"
href="https://bugs.llvm.org/show_bug.cgi?id=39728">39728</a>
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<th>Summary</th>
<td>Trivial type with defaulted assignment and destructor is not usable in constexpr
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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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>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>ldionne@apple.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<pre>The following code does not compile under Clang trunk (GCC compiles it):
----------------------------------------------------------
#include <type_traits>
struct Trivial {
Trivial& operator=(Trivial const&) = default;
~Trivial() = default;
};
static_assert(std::is_trivially_copy_assignable<Trivial>::value);
static_assert(std::is_trivially_destructible<Trivial>::value);
constexpr bool use() {
Trivial a{}, b{};
a = b;
return true;
}
static_assert(use());
----------------------------------------------------------
The command I use to reproduce is this:
----------------------------------------------------------
$ pbpaste | clang++ -std=c++2a -xc++ -fsyntax-only -
<stdin>:11:16: error: constexpr function never produces a constant expression
[-Winvalid-constexpr]
constexpr bool use() {
^
<stdin>:13:5: note: non-constexpr function 'operator=' cannot be used in a
constant expression
a = b;
^
<stdin>:4:14: note: declared here
Trivial& operator=(Trivial const&) = default;
^
<stdin>:17:15: error: static_assert expression is not an integral constant
expression
static_assert(use());
^~~~~
<stdin>:13:5: note: non-constexpr function 'operator=' cannot be used in a
constant expression
a = b;
^
<stdin>:17:15: note: in call to 'use()'
static_assert(use());
^
<stdin>:4:14: note: declared here
Trivial& operator=(Trivial const&) = default;
^
2 errors generated.
----------------------------------------------------------
Live example with Clang trunk: <a href="https://wandbox.org/permlink/gJWRWbzxfduLQnc5">https://wandbox.org/permlink/gJWRWbzxfduLQnc5</a>
Live example with GCC trunk: <a href="https://wandbox.org/permlink/jJU6pW9S6rAYdGrH">https://wandbox.org/permlink/jJU6pW9S6rAYdGrH</a>
The problem seems to be that the defaulted assignment operator is not
constexpr. I think it should be (especially since it's trivial).</pre>
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