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sebmck's profile
Sebastian
Sebastian
Sebastian
Verified account
@sebmck

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SebastianVerified account

@sebmck

JavaScript boy and “lovely thoughtleader” ⌨️ he/him ♂️

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Joined April 2011

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    Sebastian‏Verified account @sebmck 3 Jul 2019
    • Report Tweet
    • Report NetzDG Violation

    Local variable refinements are unsafe in TS and Flow. Both are bad, TS is the worst. Seems obvious in hindsight but neither handle local refinement invalidation correctly. I'm not speaking abstractly, this has caused bugs in my code before.

    2:00 PM - 3 Jul 2019
    • 2 Retweets
    • 34 Likes
    • Giovanni Gaglione busticated pizza wolf Daniel Lo Nigro Someone you follow Jesse Schalken Amir Mikhak Adam Drago Nicholas Whittaker Cateland
    4 replies 2 retweets 34 likes
      1. New conversation
      1. Sebastian‏Verified account @sebmck 3 Jul 2019
        • Report Tweet
        • Report NetzDG Violation

        Flow at least invalidates refinements when calling local functions that mutate variables, but does not follow any indirection https://flow.org/try/#0PQKgBAAgZgNg9gdzAZwC4CcCWBjVYTABQhMApngG4CGMAXGAHYCuAtgEanpgA+KGmDAOZgAvGADk4gNzEoTBrkxwGYKsmSZBDAJIMAJpnSlFygBQBKMAG9CYVes0MAcqw7oLMgL6z5JlWo0tF3ZOC2tbMGoYUTAAJi8fBVQlFRYqATCbO0woMFNUAE8AB1I4XKjRETFxZhD0cUssuzBUAAt0REZSJABRdA73cSc4RldOZFUYeARSPQaZO28I4GAwbVy2zAmENTAAAwDHYLc9ltbSFQAxabAEOCYYPTBsOH7jVBgCsAEozD0qVCkM5AoxQASkFgXVARQ5aXQGIx+DzEOwrMAAFVaWxQrXujzAUHSMAANN9UOIJlRRnUIqYovQ0FghOYvEA …

        1 reply 0 retweets 18 likes
        Show this thread
      2. Sebastian‏Verified account @sebmck 3 Jul 2019
        • Report Tweet
        • Report NetzDG Violation

        TS won't ever invalidate local refinements in this case, even when it can easily statically tell that a function call will https://www.typescriptlang.org/play/#code/DYUwLgBAbghsBcEB2BXAtgIxAJwgHwgGcxsBLJAcwgF4IByOgbgChmAzFJAYzFIHskEGIUKkKSAHLos2ABQBKCAG9mEaHBoQATCwC+rDt14CIaGOQXLVEUmwiywATwAOIPndjAa1WnVSYcOkUVNTUwAAtsPgB3ZBBYgFFsKLk6CT5kaRxCIWBgGJAAEyCWNX1rAHoKiAARATpIJBAioSRHGyRC0mwQHn5BcJwQa2FRcSkAuXkWSuqAFXDSHMJwvhRgQog2c2AAGhswOhyYTMnrLgFiIhJEYjJKTU89IA …

        7 replies 1 retweet 22 likes
        Show this thread
        3. End of conversation
      2. New conversation
      1. Ryan Cavanaugh‏ @SeaRyanC 4 Jul 2019
        • Report Tweet
        • Report NetzDG Violation
        Replying to @sebmck

        The real problem is that the "safe" assumption (if you can't see a function body, assume it changes everything) is also the one most likely to be wrong in practice -- function bodies you can't see *almost never* change locally-visible data

        2 replies 0 retweets 2 likes
      2. Sebastian‏Verified account @sebmck 4 Jul 2019
        • Report Tweet
        • Report NetzDG Violation
        Replying to @SeaRyanC

        Dunno, I've found that TypeScript is way too loose. I never personally found a problem with refinment invalidation when writing code with Flow but I'm a masochistic and am fine writing weird code.

        1 reply 0 retweets 1 like
      3. 1 more reply
      1. Marcelo Retana  💻‏ @marcelo_retsal 3 Jul 2019
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        Replying to @sebmck

        Basically just let’s use react proptypes and make sure how the data is coming and going from/to the backend. Have real control over your types by yourself. Man I don’t like TS 😂

        0 replies 0 retweets 4 likes
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      4. New conversation
      1. Bob Myers‏ @bobmyers 4 Jul 2019
        • Report Tweet
        • Report NetzDG Violation
        Replying to @sebmck

        Could you please explain what you mean by "local variable refinements"?

        1 reply 0 retweets 1 like
      2. Sebastian‏Verified account @sebmck 4 Jul 2019
        • Report Tweet
        • Report NetzDG Violation
        Replying to @bobmyers

        Sebastian Retweeted Ivan Babak

        The examples included in my follow up tweets clarify. I should have said "closed-over variables" apparently:https://twitter.com/sompylasar/status/1146529893301116928 …

        Sebastian added,

        Ivan Babak @sompylasar
        Replying to @sebmck
        To be completely honest, these are not _local_ variables, these are _closed-over_ variables.
        1 reply 0 retweets 2 likes
      3. 3 more replies

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