subtyping

Extending Classes

abstract class Base {
    def foo = 1
    def bar: Int
}

class Sub extends Base {
    override def foo = 2 //must include override if you are ovveriding soething
    def bar = 3 //override opt here
}

Function Bounds

def selection[A <: Animal](a1: A, a2: A): A =
  if (a1.fitness > a2.fitness) a1 else a2

Here, “<: Animal” is an upper bound of the type parameter A.

It means that A can be instantiated only to types that conform to Animal.

Generally, the notation

• A <: B means: A is a subtype of B, and(upper bound)

• A >: B means: A is a supertype of B, or B is a subtype of A.(lowerbound)