Calling dependent method type causes AbstractMethodError #6135
Description
This issue shows up when calling abstract dependent method types declared within generic classes. The class generic parameter must appear somewhere in the method signature. For instance:
> class A{ class V }; val a1 = new A; val v1 = new a1.V
...
> abstract class B[S]{ def f(t: S, a: A)(v: a.V) }
...
> val b1 = new B[String]{ def f(t: String, a: A)(v: a.V) = println("ok!") }
...
> b1.f("",a1)(v1)
java.lang.AbstractMethodError: B.f(Ljava/lang/Object;LA;LA$V;)V
at .<init>(<console>:13)
at .<clinit>(<console>)
...I found similar problems when the parameter S appears in other locations of the method signature, i.e. the compiler also complains when f is declared either as f1 or f2 (see bellow). However, there is no problem whatsoever when the parameter is not part of the declaration, as in f3:
def f1(a: A)(t: S, v: a.V)
def f2(a: A)(v: a.V): S
def f3(a: A)(v: a.V)Still, we can get f be called successfully if object b1 is created through an object declaration:
> object b1 extends B[String]{ def f(t: String, a: A)(v: a.V) = println("ok!") }
...
> b1.f("",a1)(v1)
ok!but the problem persists when f is called through a generic function or other generic class (including B[S] itself). For instance:
scala> def f[S](b: B[S], t: S, a: A)(v: a.V) = b.f(t,a)(v)
...
scala> f(b1,"",a1)(v1)
java.lang.AbstractMethodError: B.f(Ljava/lang/Object;LA;LA$V;)V
at .f(<console>:9)
at .<init>(<console>:14)
...I couldn't find a proper workaround. Tried these but don't work either:
def f(t: S, a: At)(e: T[a.type]) // given another definition of T
def f(t: S, a: At): a.T => UnitThe last one doesn't even compile when B[String] is instantiated, showing an strange message:
> object b1 extends B[String]{ def f(a: A) = (v: a.V) => println("ok!") }
<console>:9: error: type mismatch;
found : a.V => Unit
required: a.V => Unit
possible cause: missing arguments for method or constructor
object b1 extends B[String]{ def f(a: A) = (v: a.V) => println("ok!") }