Hi, 2010/6/3 Christophe Grand <christo...@cgrand.net>
> On Thu, Jun 3, 2010 at 1:56 PM, Laurent PETIT <laurent.pe...@gmail.com> > wrote: > > If I understand things well, one problem with ruby monkey patching is > that > > if a library I use opens a class C and adds a method whose signature is M > to > > it, and if in my own code I also open the same class C and add a method > > whose signature is M to it, then the library may break because it will > call > > my implementation of M, not the librarie's original one. > > > > Now to clojure. I can see the same problem occur, while the article's > author > > claims that in clojure there's (almost) no problem anymore. > > If several libraries, including my program, redefine blindlessly a > protocol > > implementation for the same type, then the "last to speak" wins. > > So isn't the problem basically the same ? > > my 2 cents: > > The surface of the problem is reduced because of namespacing: two > different "fold" methods (with different semantics) from two protocols > won't clash. Of course. I was not thinking about that. I was talking about working on the same protocol. Here is the scenario I have in mind: clojure 1.3 ships in december with loooots of protocols for the whole set of abstractions currently implemented as interfaces. A bunch of developers all over the place start adding implementations for these protocols for types not covered by clojure itself .... > Plus if there are two extensions of the same protocol to > the same type, they should be rather equivalent since they satisfies > the same semantics. > ... granted, the more specific the semantic will be, the less different the implementations should behave. So back to my scenario: lots of people adding protocol impls for lots of "common java types" : new implementations each time, copied implementations some other time. Of course some implementations will be buggy the first time they are delivered. Depending on N libraries each providing their own implem. in a particular version could lead, depending on the order the libraries are loaded in the environment, in having sometimes a buggy version, sometimes an "almost correct version". > > I think one must only extend a protocol to a type if he owns either > the type or the protocol. > > The general example here is java.lang.String. Nobody owns it but oracle/sun (and arguably clojure itself). People will want to reimplement some clojure protocols on it, interpreting the String content in a bunch of exotic ways :). But I understand the rule : "extend with great care if you neither own the protocol nor the type". -- 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 Note that posts from new members are moderated - please be patient with your first post. 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
