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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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propensive.com
Joined July 2010

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    1. Jon Pretty‏ @propensive 20 Jul 2020

      Jon Pretty Retweeted Jon Pretty

      So, most people were wrong about this, and it also split opinion rather evenly... I suspect even that some of the people who were right were right for the wrong reasons! But the Scala compiler is actually being safe and correct, here. Explanation below...https://twitter.com/propensive/status/1284952925727580165 …

      Jon Pretty added,

      Jon Pretty @propensive
      Ok, without checking, what do you think happens? (List(0): Seq[Int]) match { case _: List[Int] => 1 case _ => 2 }
      3 replies 3 retweets 14 likes
      Show this thread
    2. Jim O'Flaherty‏ @jimofl 20 Jul 2020
      Replying to @propensive

      tl;dr Poll answer "Compiles, no warning → 1" is correct. Right?

      1 reply 0 retweets 1 like
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    4. Jon Pretty‏ @propensive 20 Jul 2020
      Replying to @jeremyrsmith @jimofl

      No, sealedness isn't required to solve it. Any as-yet-unknown subtype can still be checked at runtime as a `List[_]` and the `Int` is still known statically.

      1 reply 0 retweets 1 like
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      Jon Pretty‏ @propensive 20 Jul 2020
      Replying to @jeremyrsmith @jimofl

      Anyhow, I like that the compiler is correct here, no matter how complex the logic, and I think it should be sufficient for us humans to suspend full understanding, and just let Scalac do its thing. But unfortunately most of us learned the hard way not to be quite so trusting...

      2:17 PM - 20 Jul 2020
      • 1 Like
      • Jim O'Flaherty
      1 reply 0 retweets 1 like

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