scala , Anonymous subclass of a parametric type by the use of ClassTag context bound
Anonymous subclass of a parametric type by the use of ClassTag context bound
Question:
Tag: scala
Given a concrete class of a given trait
trait Trt {
val x: Int
}
class C extends Trt {
val x: Int = 3
}
I'd like to create an object of an anonymous class of a parametric type in order to override the attribute x
abstract class SomeClass[T <: Trt : ClassTag] {
def f: Unit = {
val original = new C
//Is this even possible?
val withOverridenX = new T { override val x = 42}
assert(original.x != withOverridenX.x)
}
}
The problem is that the compiler keeps reporting the following error:
>> Error:(26, 35) class type required but T found
Is instancing anonymous classes extenging parametric types classes even possible?
I know the problem is that T is a type and not a class and I wonder if maybe, thanks to ClassTag bounded contex, it could be possible to instantiate withOverridenX.
Answer:
You can't instantiate T since it is not known at runtime, just at compile time. The ClassTag would just give you acces to the Class object of T through the runtimeClass method. But with just that, you can't subclass T by calling new, since there's for example no evidence that T has a parameterless constructor.
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