> Cédric Paternotte wrote: > ... > > > 5. With this : > http://www.cs.utexas.edu/ftp/pub/techreports/tr01-60/tr01-60.pdf > > > > Gracjan Polak wrote: > > I've been thinking about slight generalization of this lately. Here are > my semi-backed thoughts as of now.
I should have mentioned http://homepages.cwi.nl/~ralf/OOHaskell/src/PoorMens2/ (again *not* using OOHaskell) The actual example encodes Chris Rathman's shape benchmark. The underlying story is somewhat similar to Gracjan's email. Compared to the code that Gracjan posted, - this code pinpoints another issue of this poormens' approach: get_super is quite obviously not enough if you end up wanting mutable objects. You need a setter as well. (My feeling here is that the encapsulation could be better. It would need coding effort to avoid that all data is public.) - this code also shows how the "fake inheritance through data composition" approach blends with virtual methods: one uses an extra class per abstract/virtual method. (Clearly, one can potentially try to bundle some methods in a class.) An issue here is that client code might get bloated with constraints: for datatype subtyping *and* all used virtual methods. Alternatively, one can place the OO methods (their functional counterparts) in the data capsules themselves! Then you get into the trouble of self references. A more general and preliminary observation: the entire approach is potentially more about object *composition* (and perhaps delegation) rather than inheritance. Many OO evangelists consider inheritance as a concept that was used too much in early OO times, while object composition is often more appropriate and flexible. So one *might* say that this approach does not encode a Java-inheritance solution but it does an inheritance-to-object-composition migration on the fly. So what Gracjan calls "Inherits" (and I call subtyping or substitution) is perhaps more a "delegates". Ralf _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
