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A comment on The Unsound Playground: Java and Scala's Type Systems are Unsound. Parent comment

Re:The Unsound Playground: Java and Scala's Type Systems are... by emmelaich on Sunday November 27, 2016 @05:42PM (#13052061)
I think it is a fundamental.

Just because D isa B it does not mean list(D) isa list(B).

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Re:The Unsound Playground: Java and Scala's Type Systems are... by prodigal_erik on Sunday November 27, 2016 @07:45PM (#13052631)
What we need is

  listContaining(Dog) isa listContaining(Animal)
  listAccepting(Animal) isa listAccepting(Dog)
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Re:The Unsound Playground: Java and Scala's Type Systems are... by STRML on Sunday November 27, 2016 @09:11PM (#13052944)
Which is precisely the idea of covariant getters / contravariant setters in some sounder languages.
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Re:The Unsound Playground: Java and Scala's Type Systems are... by Kreeg on Monday November 28, 2016 @06:36AM (#13054789)
IIRC, Scala has covariant/contravariant generics

(apologies for the bad terminology, I'm not too familiar with the details)

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Re:The Unsound Playground: Java and Scala's Type Systems are... by Groxx on Wednesday November 30, 2016 @12:28AM (#13068695)
support for "<? extends X>" and "<? super X>" is supporting covariant / contravariant. invariant would be "<x>".

basically. the same concept applies in a number of areas, with varying support (e.g. Java doesn't support contravariance in its method overloading: http://stackoverflow.com/a/2501513/16295 )

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