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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Operator overload matching failure with enum as first operand"
href="https://bugs.llvm.org/show_bug.cgi?id=40329">40329</a>
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<th>Summary</th>
<td>Operator overload matching failure with enum as first operand
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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
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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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++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>Kevin.Bracey@arm.com
</td>
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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>Created <span class=""><a href="attachment.cgi?id=21334" name="attach_21334" title="Compilable example">attachment 21334</a> <a href="attachment.cgi?id=21334&action=edit" title="Compilable example">[details]</a></span>
Compilable example
The attached code using a C++98-compatible "SafeEnum" compiles and "works" with
all other compilers tried than clang. I say "works" because it isn't really
"safe", but it at least compiles.
In summary, we have
template<typename Target, typename LayoutType = unsigned int>
struct SafeEnum {
/**
* Type of the representation.
*/
typedef LayoutType representation_t;
/**
* Construction of an enumeration value.
*/
SafeEnum(LayoutType value) : _value(value) { }
friend bool operator!=(SafeEnum lhs, SafeEnum rhs);
};
struct hci_error_code_t : SafeEnum<hci_error_code_t, uint8_t> {
enum type {
SUCCESS = 0x00
};
hci_error_code_t(type value);
explicit hci_error_code_t(uint8_t raw_value);
};
hci_error_code_t hci_status;
Then, all compilers will accept
if (4 != hci_status) // so much for type safety
or
if (hci_status != hci_error_code_t::SUCCESS)
But clang alone will not accept
if (hci_error_code_t::SUCCESS != hci_status)
It seems the overload using the argument conversion from hci_error_code_t::type
-> uint8_t -> SafeEnum<hci_error_code_t, uint8_t> isn't found if it's the first
argument, but is if it's the second.
Clearly the SafeEnum class doesn't do what is intended, and can be replaced by
`enum class`, but it seems something is off in clang's overload resolution - I
can find no reason in why argument order should matter here.</pre>
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