Somebody must have asked this before! Is there anybody
who can claim to have written a Lua program that uses
a table whose keys are neither numbers nor strings,
and for which this feature is essential?
Perhaps Lua's Registry itself, when registering metatables and any other
resource? I know that there might be work-arounds, but I think none of
them are as fast as it is now, specially because you would have to hash
objects from/to string/number to be used as table keys.
I can't imagine myself without this feature (table keys as any non-nil
value), nowadays :)