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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 - Clang++ fails to instantiate std::optional if type has a enum class field"
href="https://bugs.llvm.org/show_bug.cgi?id=50904">50904</a>
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<th>Summary</th>
<td>Clang++ fails to instantiate std::optional if type has a enum class field
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</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>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>florin@signbit.net
</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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<pre>Using clang trunk:
Debian clang version 13.0.0-++20210619101720+e1adf90826a5-1~exp1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Candidate multilib: .;@m64
Selected multilib: .;@m64
The following program fails to compile:
#include <optional>
class Bar
{
public:
struct Foo
{
#if WANT_TO_SEE_IT_FAIL
enum class Toast
{
Alpha,
Beta,
Gamma
};
Toast aToast = Toast::Beta;
#endif
int someInt;
};
std::optional<Foo> theFoo;
};
int main()
{
Bar aBar;
aBar.theFoo = std::make_optional<Bar::Foo>();
return 0;
}
$ clang++-13 -std=c++17 -DWANT_TO_SEE_IT_FAIL test_std_optional_fail.cpp
(main)clang_limitations
test_std_optional_fail.cpp:29:18: error: no matching function for call to
'make_optional'
aBar.theFoo = std::make_optional<Bar::Foo>();
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/optional:1269:5:
note: candidate template ignored: requirement 'is_constructible_v<Bar::Foo>'
was not satisfied [with _Tp = Bar::Foo, _Args = <>]
make_optional(_Args&&... __args)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/optional:1261:5:
note: candidate function template not viable: requires single argument '__t',
but no arguments were provided
make_optional(_Tp&& __t)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/optional:1277:5:
note: candidate function template not viable: requires at least argument
'__il', but no arguments were provided
make_optional(initializer_list<_Up> __il, _Args&&... __args)
^
1 error generated.
If we don't define WANT_TO_SEE_IT_FAIL then the program compiles.</pre>
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