Kotlin sealed classes - why doesn't compiler check for all subtypes?

Question

When using sealed classes, the compiler only checks for subtypes in the same file.

One of the big selling points of sealed classes is the exhaustive checks when using a when expression. So why isn't this implemented?

In 1 file I have:

class C : B()

In another file I have:

sealed class A

open class B : A()

fun switch(input: A) =
    when(input) {
        is B -> Unit
//        is C -> Unit - I expect a compiler error since this is a subtype and it's commented out
    }

The first case - `is B` covers all subclasses of B. There is no need to `C`. But you may have `is C` case before `B`, than it will make sense — Eugene Petrenko, Jan 23 '19 at 19:51
Oh, I totally missed that C is a B so `is B` covers it. Thanks! — Ivan, Jan 24 '19 at 00:46

score 0 · Accepted Answer · answered Jan 24 '19 at 00:53

0

As Eugene Petrenko commented, the is B case that is required by the compiler covers all subclasses of B.

answered Jan 24 '19 at 00:53

Ivan

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Kotlin sealed classes - why doesn't compiler check for all subtypes?

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