Scala-嵌套类型关键字

Question

I was going through Akka source code, and I came across the following

type Repr[+O] <: FlowOps[O, Mat] {
   type Repr[+OO] = FlowOps.this.Repr[OO]
   type Closed = FlowOps.this.Closed
}
type Closed

Can someone explain me what's going on here ??

Answer 1

FlowOps[O, Mat] {
   type Repr[+OO] = FlowOps.this.Repr[OO]
   type Closed = FlowOps.this.Closed
}

is a compound type with a refinement . Namely, FlowOps[O, Mat] by itself can have any Repr and Closed type members; here we require specific ones. This type is used as an upper bound for the type member type Repr[+O] .