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propensive's profile
Jon Pretty
Jon Pretty
Jon Pretty
@propensive

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Jon Pretty

@propensive

Supporting Scala through professional training and open-source software. Responsible for Magnolia, Fury, Scala World and Functional Africa.

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Joined July 2010

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    1. Jon Pretty‏ @propensive 19 Aug 2018

      This will get you a compiler crash in every version of Scala 2.x. I'm surprised I never noticed this before. Is there a ticket for this already? trait X { type Z } trait Y { type Z } type A = X { type Z = Int } type B = Y { type Z = Char } implicitly[A with B =:= B with A]

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    3. Paolo G. Giarrusso‏ @Blaisorblade 20 Aug 2018

      First, we don’t have a perfect story, but type equality is transitive *if you construct the proof* by explicitly using the (A with B)#Z. It’s a bit like the difference between “definitional” and “propositional” equality, tho both are transitive there.

      1 reply 0 retweets 1 like
    4. Paolo G. Giarrusso‏ @Blaisorblade 20 Aug 2018
      Replying to @Blaisorblade @contrarivariant @propensive

      Second, (A with B) is empty, so (A with B)#Z should be rejected when actually using it. One bugfix from Martin here (https://github.com/lampepfl/dotty/pull/4036 …) has stalled (in part my fault), I’ll check what happens here.

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      Jon Pretty‏ @propensive 20 Aug 2018
      Replying to @Blaisorblade @contrarivariant

      Appears to make some sense, but I'll have to spend some time thinking about it some more... ;)

      4:54 AM - 20 Aug 2018 from Stockport, England
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