[Checkers] Comments on Prototype hierarchy
mahmood at MIT.EDU
Tue Jun 2 14:39:29 EDT 2009
> When in particular does a programmer want to use the bottom qualifier?
> I believe you, but some concrete examples would be useful.
In practice, this is an issue under two conditions:
1. typical condition: There is a value that is a subtype of
everything, e.g. null value for most checkers.
2. additional condition: the hierarchy is not a single-line hierarchy,
i.e. there are some incomparable qualifiers. Otherwise, a bottom
exists by default.
As for examples, the only one I can think of now is handling null in
almost all checkers (e.g. IGJ, Prototype-NonPrototype-PrototypeOrNot,
I can see how numerical literals would be bottom values as well for
some unit qualifiers, e.g. DistanceInMile-DistanceInKm.
> That sounds possibly reasonable. Should it be built into every
> checker by
> default, including the basic checker? Should it have a standard name?
I think that the proper solution to output a debugging statement if a
single bottom doesn't exist. The bottom values differ depending on
> I see @Prototype as as aberration. Any use must be explicitly
> noted, even
> in a method body. I am happy that
> Invariant inv = new @Prototype Invariant(...);
> is invalid. This should be written as
> @Prototype Invariant inv = new @Prototype Invariant(...);
Sounds good with me.
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