Error

[error] .../App2.scala:9: type mismatch;
[error]  found   : input.type (with underlying type H#Input)
[error]  required: RouteService.this.Holder.Input
[error]   def extractFoo(input: H#Input): Foo = Holder.input2Foo(input)
[error]                                                          ^
[error] one error found
[error] (core/compile:compileIncremental) Compilation failed
[error] Total time: 0 s, completed Oct 23, 2016 11:15:51 PM

Question.scala

class Foo

sealed trait HolderInterface {
  type Input
  def input2Foo(resp: Input): Foo
}

class RouteService[H <: HolderInterface](val Holder: H) {
  def extractFoo(input: H#Input): Foo = Holder.input2Foo(input)
}