subclass stuff

subclass stuff

there can be a thing that is a subclass of two parent classes-- a Mermaid is a Fish and a Person
how about a Furniture and a Vehicle? wheelchair

class Foo extends Bar implements I1,I2,I3... (this is Java)

Scala--
class Foo extends Bar with T1, T2, T3...
trait T1... etc etc

Which do you pick if both parents have the same method with different implementations?
"overloading"

def foo(x:Int)
def foo(x:Int, b:Boolean)

and that is how you tell them apart

how do you decide?
- alphabetical? depth of parent? fastest? pick from first parent listed?
- or, programmer must specify

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class Foo
  val x
  def f(): Mammal
  def g(x: Mammal): Unit

class Bar extends Foo
  def f(): Cat                // this is covariance -- methods only
  def g(x: Animal): Unit      // this is contravariance -- parameters only