TypeScript 3.5 - Hackdot

Re:TypeScript 3.5 by tomp on Thursday May 30, 2019 @02:02AM (#20048783)

Probably... but in any case TypeScript also supports naked (edit: I just made up the name) unions, where you don't need to declare them upfront, and where values of different types can be included directly. Such as:

  let a = random() ? 'a' : 1

TypeScript infers type

  string | number

[ Parent | on HN ]

Re:TypeScript 3.5 by marton78 on Thursday May 30, 2019 @06:54AM (#20049936)

This is still a discriminated union, only that the discriminator is provided by Javascript and is thus hidden: it's `typeof`.

[ Parent | on HN ]

Re:TypeScript 3.5 by tomp on Thursday May 30, 2019 @08:17AM (#20050387)

Yeah, that's the runtime perspective... but for the type system, they're different... with the "naked" union being much harder (as they're non-algebraic - `a | b | b` always equals `a | b` and might even equal just `a` for some values of `a` and `b`)

[ Parent | on HN ]

Re:TypeScript 3.5 by spion on Thursday May 30, 2019 @12:09PM (#20052632)

No, this works on any overlapping types too - even unsound combinations such as `T | Array<T>`

[ Parent | on HN ]