Re: [TYPES] Why cannot declare a super type dynamically?
Jeremy Siek <[email protected]>
| Newsgroups | gmane.comp.science.types |
|---|---|
| Message-ID | <[email protected]> |
[ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list ] Dear Xuhui, Here’s a few related papers from the late 1990’s. Signatures: A language extension for improving type abstraction and subtype polymorphism in C++ Gerald Baumgartner, Vincent F. Russo https://doi.org/10.1002/spe.4380250803 <https://doi.org/10.1002/spe.4380250803> Implementing signatures for C++. Gerald Baumgartner and Vincent F. Russo. 1997. ACM Trans. Program. Lang. Syst. 19, 1 (January 1997), 153-187. http://dx.doi.org/10.1145/239912.239922 <http://dx.doi.org/10.1145/239912.239922> Safe structural conformance for Java. by Laufer, Baumgartner, and Russo. The Computer Journal, 43(6) 2000. Cheers, Jeremy > On May 26, 2019, at 9:27 PM, Xuhui Li <[email protected]> wrote: > > [ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list ] > > Dear All, > > > As far as I know, the existing type systems allow the subtyping being declared in the defintion of the sub types but forbid the super type being declared after the subtype . For example, class A extends B. However, if a new type C is declared and it is found that conceputually C should be a supertype of A (assume that the fields of C don't occur in A but an injection of the fields can be defined) , we cannot declare A extends C after A has been already defined. Why cannot this happen? Will dynamically introducing a supertype threaten the safety of existing type system? > > > Thanks for your attention. > > > Best Regards > > > Xuhui