Why doesn't Scala fully infer type parameters when type parameters are nested?

Question

Consider the following Scala code:

abstract class A
abstract class B[T <: A]
class ConcreteA extends A
class ConcreteB extends B[ConcreteA]

class Example         


        

Answer 1

I have composed a document of type inference workarounds on GitHub for my own learning.

A few simple rules that I find useful are:

• Type parameters of type parameters cannot be inferred: Scala type inference only sees types specified in the parameter list (not to be confused with type parameter list).

• Previous parameters are not used to infer future parameters: Type information only flows across parameter lists, not parameters.

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However, in this particular example type members are the way forward (thanks @Kipton Barros!)