https://bugs.llvm.org/show_bug.cgi?id=40329
Bug ID: 40329
Summary: Operator overload matching failure with enum as first
operand
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: kevin.bra...@arm.com
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
Created attachment 21334
--> https://bugs.llvm.org/attachment.cgi?id=21334&action=edit
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.
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