VarianceWithBounds

VarianceWithBounds.scala

class Super
class Sub extends Super
class SubSub extends Sub

class InvariantSubType[A]{
  def method[B <: A](value :B) = value
}

val invariantSubType1 = new InvariantSubType[Sub]
val res1 = invariantSubType1.method(new SubSub)

val invariantSubType2 = new InvariantSubType[SubSub]
//val res2 = invariantSubType2.method(new Sub)  // not a subtype

class InvariantSuperType[A]{
  def method[B >: A](value :B) = value
}

//implicit def a2b(a:Sub) = new SubSub

val invariantSuperType1 = new InvariantSuperType[Sub]
//val res12:SubSub = invariantSuperType1.method(new SubSub)  // SubSub is not Super Type

val invariantSuperType2 = new InvariantSuperType[SubSub]
val res13 = invariantSuperType2.method(new Sub)

class UpperBound[+A]{
  def method[B >: A](value :B) = value
}

val test2242 = new UpperBound[Sub]
//val res:SubSub = test2242.method(new SubSub) // SubSub is not Super Type

val test2122:UpperBound[SubSub] = new UpperBound[SubSub]
val res1:Sub = test2122.method(new Sub)


class UpperBound[-A]{
  def method[B <: A](value :B) = value
}

val test224 = new UpperBound[Sub]
val res:SubSub = test224.method(new SubSub)
val test2123:UpperBound[SubSub] = new UpperBound[SubSub]
//val res1:Sub = test2123.method(new Sub)  // Not a Subtype