Union type subtyping in Scala -

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i can following dotty: 

trait ex {type t <: int | seq[int]; def f:t}  trait ex2 extends ex {override type t = seq[int]; override def f = seq(2)}  trait ex3 extends ex {override type t = int; override def f = 2}

how can union type subtyping without dotty?

the simple solution upper bound type:

trait ex {type t >: int seq[int]; def f:t}  trait ex2 extends ex {override type t = seq[int]; override def f = seq(2)}  trait ex3 extends ex {override type t = int; override def f = 2}

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