Hi Tassilo, Thanks for the reply.
The thing is, although the implementations for extending protocols directly in records and with extend-type might be different, there is no reason why the syntax should be different: from Clojure-programmer perspective it’s all the same. It is a leaked abstraction if we have to thing about those details. The same applies for interface implementation: overloaded methods there and multi-arity functions in Clojure shouldn’t look differently to a Clojure programmer (unless there is some more profound difference). Best regards, Alexey On 13 May 2015 at 14:46, Tassilo Horn <t...@gnu.org> wrote: > 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.
