oop - Parameterizing Scala Method With Parameterized Generic Class Fails -


this: 

trait simplejob[+t <: serializable, +r <: serializable]  {   def dostuff[t](message : t) : r }  object simplejob {   def get_or_create_job(name : string) = print("do stuff")    def apply[t, r](name : string, message : t) : future[r] = future{"do stuff".asinstanceof[r]}    def apply[s <: simplejob[t, r]](message : t) : future[r] = this(classof[s].getname, message) }

fails compile because compiler cannot resolve t, r, or s in second apply method.

note on example: i've taken out of function bodies make minimally reproducible. example fail if r not string. if interested, attempted make structure limited form of type-safe akka actor. idea simplejob subclassed , parameterized, , messages of subclass actors passed through object calls of form simplejob[actorsubclasstype].apply(message), parameter , return value type-safe. apply methods check if actor given class had been instantiated, created if had not, , pass message , return future reply. turned out not feasible number of reasons, along way realized there didn't understand scala's inhereitance system , i'm trying find out don't go down similar rabbit holes again.

if add 2 parameters this:

def apply[s <: simplejob[t, r], t, r](message : t) : future[r] = this(classof[s].getname, message)

it compiles, want able parameterize function 1 type, since resolves other types.

i'd appreciate if me understand i'm apparently misunderstanding scala's type system.

thanks in advance.

the problem in def apply[t, r, s <: simplejob[t, r]](message: t): future[r] s type not used in method arguments @ all, naturally not allow compiler infer concrete value of s given arguments , vice versa. if passing instance of simplejob method, situation opposite - compiler able infer argument types:

def apply[t, r, s <: simplejob[t, r]](sj: simplejob[t, r])                                      (message: t): future[r] = ???

alternatively, can use abstract type members instead of type parameters:

trait simplejob {   type t <: serializable   type r <: serializable   def dostuff[t](message: t) : r }  object simplejob {   def apply[s <: simplejob](message: s#t)(implicit sct: classtag[s]): future[s#r] =      future { println(sct.runtimeclass.getname); ??? } }

note cannot use classof[s] when s type parameter; generics in jvm not reified, therefore have use class tag machinery work around it.


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