Autoclose with for comprehensions

autoclose.scala

object closable {
  type Closable = { def close }
  class Autoclose[A <: Closable](c: A){
    def foreach(f: A => Unit) = {
      try { f(c) }finally { c.close }
    }
  }
  case class Connection(name:String) {
    def close = println("closing " + this) 
  }
  case class Statement(c: Connection,q :String){
    def close = println("closing " + this)
    def exec = println("executing " + q + " on " + c)
  }
  implicit def autoClosable[A <: Closable](c: A) = new Autoclose(c)
  def test = for(c <- Connection("conn"); 
		 st <- Statement(c,"select * from table")){
		   st.exec
		 }
}


-- execution

scala> closable.test
closable.test
executing select * from table on Connection(conn)
closing Statement(Connection(conn),select * from table)
closing Connection(conn)

That's amazing. Monad in the box. Beautiful.

It's a pity that to generalize it to any side effect it would probably require dependent types; and this specific examples with close() demonstrates the trick better, but I wonder if we could generalize it to any post-action... it looks pretty similar to state monad.

Thanks anyway; it was an eye-opener to me.