Scala Traits - A Comprehensive Guide

What are Scala Traits?

Traits are abstract classes that are meant to be added to some other class. A trait adds some methods or fields to an unknown parent class. It encapsulates field and method definitions which can be reused by adding them into classes. Unlike class inheritance in which each class must inherit from just one superclass whereas a class can mix in any number of traits. A trait defines the object types by specifying the signature of the supported methods.

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e.g.

trait IntegerSet {
def incl(x: Int): IntSet
def contains(x: Int): Boolean
}
class EmptySet extends IntegerSet {
def contains(x: Int): Boolean = false
def incl(x: Int): IntSet = new NonEmptySet(x, new EmptySet, new EmptySet)
}

One trait can also extend another trait like as follows:

e.g.

trait Almirah {
def canOpen(p: Person) : Boolean =
return true
def canPass(p: Person) : Boolean =
return true
}
trait Locked extends Almirah {
override def canOpen(p: Person): Boolean = {
if (!p.hasItem(theKey)) {
println("You don't have the Key")
return false
}
println("Using key...")
return super.canOpen(p)
}
}