http://llvm.org/bugs/show_bug.cgi?id=11428
Bug #: 11428
Summary: errc, io_errc and future_errc constants should really
be scoped enums
Product: libc++
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P
Component: All Bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 7641
--> http://llvm.org/bugs/attachment.cgi?id=7641
Patches for header files <system_error>, <future> and <ios>
The enumeration types errc, io_errc and future_errc are defined in the standard
with "enum class", but currently libc++ defines them as regular enums nested in
a struct. Although I understand that the struct+enum hack is more portable,
having scoped enumerations is essential for compiling even the following simple
code:
void f(error_condition c)
{
if (c == errc::invalid_argument)
{ /* ... */ }
}
that's because if errc::invalid_argument is a regular enum value it decays to
int and operator== becomes ambiguous. On the other hand, if it is a scoped enum
value, the only operator== available is the correct one, with signature:
bool operator==(const error_condition& lhs, const error_condition& rhs)
noexcept;
(errc::invalid_argument being implicitly converted to error_condition because
of the is_error_condition_enum<> machinery).
I therefore suggest to use scoped enums wherever specified by the standard. I
am attaching patches that accomplish that unconditionally. A possible backward
compatible approach could be to add a __has_feature(cxx_strong_enums) check,
although it has to be noted that we already used scoped enumerations in
<condition_variable> without any check.
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