I encountered andThen
, but did not properly understand it.
To look at it further, I read the Function1.andThen docs
def andThen[A](g: (R) ⇒ A): (T1) ⇒ A
mm
is a MultiMap instance.
scala> mm
res29: scala.collection.mutable.HashMap[Int,scala.collection.mutable.Set[String]] with scala.collection.mutable.MultiMap[Int,String] =
Map(2 -> Set(b) , 1 -> Set(c, a))
scala> mm.keys.toList.sortWith(_ < _).map(mm.andThen(_.toList))
res26: List[List[String]] = List(List(c, a), List(b))
scala> mm.keys.toList.sortWith(_ < _).map(x => mm.apply(x).toList)
res27: List[List[String]] = List(List(c, a), List(b))
Note - code from DSLs in Action
Is andThen
powerful? Based on this example, it looks like mm.andThen
de-sugars to x => mm.apply(x)
. If there is a deeper meaning of andThen
, then I haven’t understood it yet.
andThen
is just function composition. Given a function f
val f: String => Int = s => s.length
andThen
creates a new function which applies f
followed by the argument function
val g: Int => Int = i => i * 2
val h = f.andThen(g)
h(x)
is then g(f(x))