cap.pony

class Foo
  var i: USize = 0
  fun ref boom() => i = 3

actor Main
  new create(env: Env) =>
    let a: Foo val = Foo
    env.out.print(a.i.string())
    bla[Foo val](a)
    env.out.print(a.i.string())
   
  fun bla[A: Foo #read](x: A) =>
    x.boom()