5 ms·
It's kind of amusing reading this as a Typescript dev because I'm so used to Typescript's expressiveness I couldn't really work out which trick it was trying to
by Vanit 6y ago
It's kind of amusing reading this as a Typescript dev because I'm so used to Typescript's expressiveness I couldn't really work out which trick it was trying to tell me was novel.
The answer is structural typing (aka duck typing).
- pd-andy 6y agoNot quite. I guess in some ways phantom types achieve the opposite of structural typing. In a language with structural typing, two types are considered equivalent if they share the same structure. With phantom types we can have a single structure and disambiguate between different uses without touching the underling structure. There's no difference between Id(User) and Id(Post) at runtime, the annotation is purely a compile-time restraint. In fact, because of typescript's structural typing, the only way to use phantom types in ts is to have some dummy field of type `never` that the type system can use to disambiguate between the two [1]. [1]: https://gist.github.com/GoNZooo/243b23702df1fae38c966ae18832c690 https://gist.github.com/GoNZooo/243b23702df1fae38c966ae18832...
- mushishi 6y agoHoly smokes, that would be irritating :D Btw. is there a difference between these two: (s: string): PlainText => <PlainText><any>s; (s: string): PlainText => s as any as PlainText; Syntax-wise I'd rather use the latter for it's more clear in typed JSX-context.
- pd-andy 6y agoAs far as I know those two are equivalent. Definitely slightly clunkier, but is what it is.
- timdeve 6y agoYes, exactly, it's because of Structural Typing that you have to implement Phantom Types in that hacky way rather than Structural Typing being the "trick".
- deleted 6y ago[deleted]