[llvm-dev] ArgList flag values

[David Greene via llvm-dev]

I've come across a need to know whether an option was set true, false or
unspecified.  If it is true I want to do one thing, if it is false I
want to do something else and if it is unspecified I want to do nothing.

ArgList::hasFlag is a convenient way to check true/false with a default
value.  An ArgList::hasFlag that returned Optional<bool> would allow
checking the unspecified case.  Returning some kind Tribool class object
would allow the same.

Both Optional<bool> and Tribool are somewhat overkill for this kind of
thing as I really wouldn't need to do comparisons and logical operations
on the value.  A three-state enum (class) would do just as well.

Is there an existing way to handle this kind of flag?  If not, would
there be interest in adding support for it?

                         -David