How to distinguish between objects with different abstract type fields?

Question

Assume, we have an abstract class with an abstract type field:

abstract class A {type T}

Now let\'s assume, we have a method, which returns

Answer 1

You can use the <%< which tells you in compile-time if two types are compatible.

scala> class A { type T }
defined class A

scala> implicitly[A { type T=String } <%< A { type T=Int } ]
:9: error: could not find implicit value for parameter e: <%<[A{type T = String},A{type T = Int}]
              implicitly[A { type T=String } <%< A { type T=Int } ]
                        ^

scala> implicitly[A { type T=String } <%< A { type T=String } ]
res1: <%<[A{type T = String},A{type T = String}] = 

scala> implicitly[A { type T=String } <%< A ]
res3: <%<[A{type T = String},A] =