Question

My game has

class Enemy

who’s AI/functionality I can change with

trait Moving
trait VerticalMover extends Moving
trait RandomMover extends Moving

and so on. Now I need to fetch preloaded stuff based on trait. What I would like to do is have a Map that accepts all traits that extend Moving as keys and then some EnemyContainer as value that would have trait related content preloaded.

But how do I define such a Map and how do format my .get() to get the container by an instance of some Enemy. Something like:

val myEnemy = new Enemy with RandomMover 
val myDetails:EnemyContainer = enemyDetailsStore.get(myEnemy.getClass)

Answer 1

Well, I assume that your enemy details store is of type Map[Class[_ <: Moving], EnemyDetails]. I suspect that something like:

//gives a Map[Class[_ <: Moving], EnemyDetails] for all matching keys
enemyDetailsStore.filterKeys(_ isInstance myEnemy) 

Or:

//Iterable[EnemyDetails]
enemyDetailsStore collect { case (c, d) if c isInstance myEnemy => d }

Or even just:

//Option[EnemyDetails]
enemyDetailsStore collectFirst { case (c, d) if c isInstance myEnemy => d }

Will do for you. The only “issue” with this code is that it’s O(N), in that it requires a traversal of the map, rather than a simple lookup, which would be O(1), or O(log N)