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error: illegal inheritance from sealed class List

1 reply on 1 page. Most recent reply: Apr 19, 2017 1:24 PM by John Lee

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John Lee

Posts: 2
Nickname: greentea
Registered: Apr, 2017

error: illegal inheritance from sealed class List

Posted: Apr 19, 2017 9:11 AM

I am trying out the examples in the book from Section 22.1 and am getting this error

error: illegal inheritance from sealed class List

These classes don't compile so I'm confused as to why they're included as examples? Am I missing something here?

case object Nil extends List[Nothing] {
override def isEmpty = true
def head: Nothing =
throw new NoSuchElementException("head of empty list")
def tail: List[Nothing] =
throw new NoSuchElementException("tail of empty list")
}

final case class ::[T](hd: T, tl: List[T]) extends List[T] {
def head = hd
def tail = tl
override def isEmpty: Boolean = false
}

John Lee

Posts: 2
Nickname: greentea
Registered: Apr, 2017

Re: error: illegal inheritance from sealed class List

Posted: Apr 19, 2017 1:24 PM

Never mind. I see now they are defining their own List class as

abstract class List[+T] {
def isEmpty: Boolean
def head: T
def tail: List[T]
}

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