7. Type Variance

[justjoheinz]

I think this section is either wrong or misleading:

This means that if you have a container defined as Box[A], and then use it with a Fruit in place of the type parameter A, you will not be able to insert an Apple (which IS-A Fruit) into it.

Of course I can do:

case class Box[A](value : A)
var xf : Box[Fruit] = Box(Apple)

but cannot do:

val xa : Box[Apple.type] = Box(Apple)
xf = xa

Maybe the sentence should read along the lines of:

This means that if you have a container defined as Box[A], and then expect a Box[Fruit], you will not be able to use Box[Apple], which is a fruit, because Box is invariant in the type parameter A.

And I just want to mention that the blog post is a very nice resource! I come to it or refer it fairly frequently. Thanks for putting it up.

[ktoso]

You're right on the wording! Would you be able to submit a PR addressing this? Thanks a lot in advance!