Alexey Cherkaev <alexey.cherk...@gmail.com> writes: Hi Alexey,
> If you have a protocol > > (defprotocol Foo (foo [x] [x y])) > > and implement it for the record > > (defrecord Bar [p q r] > Foo > (foo [x] x) > (foo [x y] [x y])) > > you write each method separately. The same is true for extend-type. > Yet, if you use extend-protocol syntax is more like usual Clojure > multi-arity function definition: > > (extend-protocol Foo > Bar > (foo > ([x] x) > ([x y] [x y]))) > > The first question is why there is a difference? I think, the difference is that deftype/defrecord create an interface (and an implementation class) under the hoods, and there, the different arities of foo are actually different methods. extend/extend-type/extend-protocol dynamically extend a protocol to some type. Basically, the protocol's underlying dynamic dispatch table gets a new [type impl-function] entry where impl-function is a real Clojure function, thus you must specify all arities you want to support the normal Clojure way. > Secondly, if you mess up which syntax is where, the error you will get > is quite obscure, nothing guards you against essentially a *wrong > syntax*: both extend-type and extend-protocol are macros, so it > shouldn’t be too difficult to add a quick check on correctness. Yeah, for extend-protocol/extend-type the standard multi-arity syntax is the only correct one. > But lastly, wouldn’t it be better to have a uniform syntax? The problem is that defrecord and deftype also allow for implementing interfaces. If Foo above was an interface, foo with 1 argument and foo with 2 arguments are completely separate methods (ok, they overload), thus it makes sense to define them separately. However, if Foo was a protocol, it would also make sense to notate it as multi-arity function. But then you have an inconsistent syntax inside defrecord/deftype. Well, although one could argue that this was a good thing because it would allow to see immediately if Foo was a protocol or an interface. Bye, Tassilo -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
