+
+ # Can a class of kind `self` specializes a class of kine `other`?
+ fun can_specialize(other: MClassKind): Bool
+ do
+ if other == interface_kind then return true # everybody can specialize interfaces
+ if self == interface_kind or self == enum_kind then
+ # no other case for interfaces
+ return false
+ else if self == extern_kind then
+ # only compatible with themselve
+ return self == other
+ else if other == enum_kind or other == extern_kind then
+ # abstract_kind and concrete_kind are incompatible
+ return false
+ end
+ # remain only abstract_kind and concrete_kind
+ return true
+ end