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Comment by pd-andy

Not 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/243b23702df1fae38c966ae18832...

parent pd-andy 5 years ago

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