I have some nested case classes that may look like the following:
case class Lowest(intVal: Int, stringVal: String)
case class Mid (lowestSeq: Seq[Lowest])
case class High (midSeq: Seq[Mid])
So if I had a class of Mid I could easily do
myMid.lowestSeq.filter(_.intVal == 42)
but I would like to create a custom filter method where I can filter Lowest elements based on a variable. I don’t mind writing some custom method like the following
case class Mid (lowestSeq: Seq[Lowest]){
def filterLowest(/*predicate*/): Seq[Lowest] = {
lowestSeq.filter(/*predicate*/)
}
}
case class High (midSeq: Seq[Mid]){
def filterLowest(/*predicate*/): Seq[Lowest] = {
midSeq.foldLeft[Seq[Lowest]](Seq.empty){case => (acc, mid)
acc :+ mid.filterLowest(/*predicate*/)
}
}
}
But I’m having a hard time understanding how I define the predicate
For example if calling on an instance of High I want to be able to do the following
val allIntValsEq42 = myHigh.filterLowest(/*???*/intVal == 42)
val allStringValsEqYo = myHigh.filterLowest(/*???*/stringVal == 42)
How can you pass in a predicate in this way for the Mid or High class?
1
Well all you need is a predicate for Lowest and a predicate is nothing more than a function that returns Boolean so all you need is:
predicate: Lowest => Boolean
But, we can improve your setup a little to make this more efficient:
final case class Lowest (intVal: Int, stringVal: String)
final case class Mid (lowestSeq: Seq[Lowest])
final case class High (midSeq: Seq[Mid]) {
def filterLowest(predicate: Lowest => Boolean): Seq[Lowest] =
midSeq.flatMap(id => mid.lowestSeq.filter(predicate))
}
Which then you can use just like when filtering the Seq directly like:
// Using placeholder syntax:
myHigh.filterLowest(_.stringVal == 42)
// Using full lambda syntax:
myHigh.filterLowest(low => low.stringVal == 42)
// Using an auxiliary function:
def lowChecker(low: Lowest): Boolean = ???
myHigh.filterLowest(lowChecker)
2