On Mar 12, 2009, at 10:59, Jeff Rose wrote: >> My main conclusion is that Clojure's system is a lot more flexible >> but also a lot more fragile. Any function can modify data of any >> "type" (as defined by metadata), even without being aware of this. > > Modifying type tags without being aware of it?
Not modifying type tags, but modifying data that has a type tag without being aware of the fact that the data has a type tag, and thus perhaps specific constraints on its contents. The most basic example is calling dissoc on a map to remove a key that is required by the semantics of the type implemented as a map. dissoc is agnostic about type tags, so it won't complain. In this specific case, struct maps can be used to prevent a key from being removed, but that's a solution only for this specific case, and not necessarily a simple one to implement. > We've heard this line of reasoning before when moving from static to > dynamic languages. If having the power to do what you want with the > language scares you, then maybe Java is a better choice. All these It doesn't scare me, otherwise I wouldn't be using Clojure. And I wouldn't be using Python as my main language either. However, I think it is important to be aware of the risks in order to watch out for them. > Adding an implementation for a new type to a multimethod is equivalent > to adding an interface implementing method to a class you defined. So > for example you could add to-string or to-xml or to-bytes or > whatever to > your own objects to make them interoperate with some existing library. > Having libraries built on top of abstract interfaces like this is > exactly what makes them interesting. I agree, of course. And yet, it is important to be aware of the consequences. For example, don't ever try to memoize the dispatching function of a multimethod - its result may well change after importing another library module. Konrad. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
