default values besides nil

[tcurdt]

This looks interesting but I think it would be nice to have default values besides nil. Maybe along the lines of:

(id)ifIsKindOfClass:(Class)aClass else:(id)value;

Not sure I like if/else naming though. Maybe this would be more expressive?

(id)nilUnlessKindOfClass:(Class)aClass;
(id)object:(id) unlessKindOfClass:(Class)aClass;