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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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    1. Sebastian‏Verified account @sebmck 22 Jun 2019
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      After using TypeScript there's some features that I'm terrified of that seem counter intuitive. All the following examples produce NO errors and are with every single strict TS option enabled.

      10 replies 6 retweets 92 likes
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    2. Sebastian‏Verified account @sebmck 22 Jun 2019
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      Type predicates are just an annotation and aren't actually checked. Meaning you can do some pretty wacky and unsafe things. Is there an technical constraint preventing TS from checking these?pic.twitter.com/qtIIzM1Cat

      9 replies 1 retweet 17 likes
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    3. Steven‏ @styfle 22 Jun 2019
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      Replying to @sebmck

      I use type predicates about as much as type casting: rarely. They’re both powerful yet unsafe. Occasionally you need to tell TS that you know better than the type system.

      1 reply 0 retweets 2 likes
    4. Sebastian‏Verified account @sebmck 22 Jun 2019
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      Replying to @styfle

      I have 12 uses of type predicates and 81 uses of "type casting". They would be even more powerful if they were safe.

      2 replies 0 retweets 1 like
    5. Steven‏ @styfle 22 Jun 2019
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      Replying to @sebmck

      If your 12 uses of type predicates is similar to your example of a string primitive, it’s actually safer to move the typeof inline as a type guard. The predicates are only useful for nested objects. It would be great if they were safe and forced an explicit cast to be unsafe.

      2 replies 0 retweets 1 like
    6. Sebastian‏Verified account @sebmck 22 Jun 2019
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      Replying to @styfle

      Here's a few instances of my usages of type predicates. It's not really an option to inline all of these, especially `isStatement`. They're essential for refinements of very large unions.pic.twitter.com/XC2FWCZls0

      1 reply 0 retweets 2 likes
    7. Steven‏ @styfle 22 Jun 2019
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      Replying to @sebmck

      The second two look fine but the isStatement can probably be achieved by using discriminated unions. If you have a switch like that, seems like you are using one property to determine the type of the object. https://www.typescriptlang.org/docs/handbook/advanced-types.html#discriminated-unions …

      1 reply 0 retweets 2 likes
      Sebastian‏Verified account @sebmck 22 Jun 2019
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      Replying to @styfle

      I left out all the other cases, there's about 50 other possible type properties that it can match.

      8:05 PM - 22 Jun 2019
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      0 replies 0 retweets 1 like

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