Brandon Elam Barker bbarker

bbarker / Example3d.scala

Created December 12, 2021 04:54

incrementation worked as expected

	List(1, 2)
	List(2, 3)

bbarker / Example3c.scala

Created December 12, 2021 04:50

do something with its members

	println(beanList3.map(_.getTheA))
	beanList3.foreach{bean =>
	bean.setTheA(bean.getTheA+1)
	}
	println(beanList3.map(_.getTheA))

bbarker / Example3b.scala

Created December 12, 2021 04:47

val anyBean: ScalaBean[Any] = bean1

bbarker / Example3a.scala

Created December 12, 2021 04:41

create a new class and a few example values

	case class ScalaBean[A](initA: A):
	private var theA: A = initA
	def getTheA: A = theA
	def setTheA(a: A): Unit = {
	this.theA = a
	}

	val bean1: ScalaBean[Int] = ScalaBean(1)
	val bean2: ScalaBean[String] = ScalaBean("Foo")
	val bean3: ScalaBean[Int] = ScalaBean(2)

bbarker / Example2h.scala

Created December 12, 2021 04:38

val outsFromInsEx: List[Outer[?]] = List(in1, in2).map(Outer.apply)

bbarker / Example2g.scala

Created December 12, 2021 04:37

the values were from a third-party library we don't control. We can emulate such behavior here

	val in1any2: Inner[Any] = (Inner("foo"): Inner[String])

	// ❌ Found: Playground.Inner[String]
	// Required: Playground.Inner[Any]

bbarker / Example2f.scala

Last active December 12, 2021 04:28

If we explicitly type the list values, then we can create our list of `Any`s

	val in1any: Inner[Any] = Inner("foo")
	val in2any: Inner[Any] = Inner(3)

	val outsFromInsAny2: List[Outer[Any]] = List(in1any, in2any).map(Outer.apply)

bbarker / Example2e.scala

Last active December 12, 2021 04:29

If we explicitly ascribe more precise types for each value, then we run into the same kind of error

	val someStuffAny2: List[SomeClass[Any]] =
	List(SomeClass("foo"): SomeClass[String], SomeClass(1): SomeClass[Int])
	// ❌ Found: Playground.SomeClass[Int]
	// Required: Playground.SomeClass[Any]
	// ❌ Found: Playground.SomeClass[String]
	// Required: Playground.SomeClass[Any]

bbarker / Example2d.scala

Created December 12, 2021 04:23

we construct a list of values that are invariant in their type parameter

val someStuffAny: List[SomeClass[Any]] = List(SomeClass("foo"), SomeClass(1))

bbarker / Example2c.scala

Created December 12, 2021 04:22

This problem would not arise if either or both of Outer or Inner had been declared with a covariant type parameter (+A) (try it), e.g.: