Thanks Allen, more than I was hoping for ... On Jun 7, 2011, at 10:11 PM, Allen Wirfs-Brock <[email protected]> wrote:
> There are lots of sources about this > > The classic but somewhat technical paper that coined the phrase that I > misquoted is William Cook's: > http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.102.8635&rep=rep1&type=pdf > > some overviews http://c2.com/cgi/wiki?SubTypingAndSubClassing > another good overview, from more of a java > perspectivehttp://www.mit.edu/~6.170/lectures/lect09-subtyping-handouts.pdf > > Basically, subtyping typically is taken to imply strict substitutability. An > instance of a subtype can be used anywhere an instance of its supertype is > expected. This isn't just about what public methods are available (a > subtype have can only add to the supertypes interface). It is also about > what can be passed to and returned form each method, recursively applied. It > is trivial to break such substitutability with JavaScript objects, even those > created by the proposed class declarations. It is possible to create > JavaScript objects that behave as subtypes but it takes work. It may not > always be worth the effort. > > Statically typed languages and their users are often very concerned about > correct subtyping because the memory safety of such languages often depends > upon the fact that subtype substitutability invariants are guaranteed. > Dynamic language folks are often less concerned because any such broken > invariants will at worst cause the program to perform the wrong computation > but dynamic runtime checks will still guarantee memory safety. Your actual > milage may vary. > > Allen > (I am not a type theorists) > > > > On Jun 7, 2011, at 8:17 PM, Kam Kasravi wrote: > >> Yes I puzzled over that a bit :) >> >> I realize that types within a typed language need to provide certain >> guarantees in terms of schema, equivalence, etc. For the those of us more >> 'untyped' than others, could you expound very briefly on the type vs class >> distinction? Is it due to javascript's ability to morph a class definition >> both in terms of its properties and its prototype chain? I also ask due to >> Dave's suggestion in relation to modules that ES.next is much more amenable >> to static analysis (paraphrasing) which I would think an IDE would exploit >> to provide some level of type-checking. In Allen's mirrors article, it seems >> like types would be important to reflection. >> Although wouldn't you know, I searched Allen's article >> (http://www.wirfs-brock.com/allen/posts/228) and he never once mentions >> 'type' :) >> >> On Jun 7, 2011, at 6:47 PM, Allen Wirfs-Brock <[email protected]> wrote: >> >>> Oops, obviously I meant: JavaScript subclassing is definitely not >>> equivalent to subtyping. >>> >>> Time for dinner-at keyboard too long. >>> >>> On Jun 7, 2011, at 6:34 PM, Mark S. Miller wrote: >>> >>>> On Tue, Jun 7, 2011 at 6:11 PM, Allen Wirfs-Brock <[email protected]> >>>> wrote: >>>> >>>> In a language as dynamic as JavaScript subtyping is definitely not >>>> equivalent to subtyping. >>>> >>>> >>>> Wow, JavaScript is even more dynamic than I thought ;). >>>> >>>> >>>> >>>> -- >>>> Cheers, >>>> --MarkM >>> >
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