Varience in scala

Seriously I never remember which is which.

Covariance

	sealed trait InMyPocket[+A]
	sealed trait Cuddler
	final case class Puppy(name: String) extends Cuddler
	object VarianceExample {
	var dog: InMyPocket[Puppy] = new InMyPocket[Puppy] {}
	var cuddler: InMyPocket[Cuddler] = new InMyPocket[Cuddler] {}
	cuddler = dog
	// dog = cuddler // doesnt compile
	}

view raw Covarience.scala hosted with ❤ by GitHub

Contravarience

	sealed trait InMyPocket[-A]
	sealed trait Cuddler
	final case class Puppy(name: String) extends Cuddler
	object VarianceExample {
	var dog: InMyPocket[Puppy] = new InMyPocket[Puppy] {}
	var cuddler: InMyPocket[Cuddler] = new InMyPocket[Cuddler] {}
	// cuddler = dog // doesnt compile
	dog = cuddler
	}

view raw Contravarience.scala hosted with ❤ by GitHub

Invariance

	sealed trait InMyPocket[A]
	sealed trait Cuddler
	final case class Puppy(name: String) extends Cuddler
	object VarianceExample {
	var dog: InMyPocket[Puppy] = new InMyPocket[Puppy] {}
	var cuddler: InMyPocket[Cuddler] = new InMyPocket[Cuddler] {}
	// cuddler = dog // doesnt compile
	// dog = cuddler // doesnt compile
	}

view raw Invarience.scala hosted with ❤ by GitHub