TypeScript types can run DOOM [video]

Re:TypeScript types can run DOOM [video] by epolanski on Wednesday February 26, 2025 @03:06PM (#43187617)

Sure, there's many other ways to type it, but none adds any kind of additional safety or strictness over Record<any, any> which was my point that `any` is the correct type in many cases, except when it widens a type.

But in my case it's not widening anything, in Record<A, B>, B can already be `any`thing.

People tend to see it as an unsafe escape hatch (which is how it is abused), but it's just a set of all possible types.

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Re:TypeScript types can run DOOM [video] by matt_kantor on Wednesday February 26, 2025 @05:17PM (#43188889)

> it's just a set of all possible types

`unknown` is the set of all possible types (it's the top type[0]). `any` goes beyond that—it basically turns off the type checker[1][2].

[0]: https://en.wikipedia.org/wiki/Top_type

[1]: https://tsplay.dev/mA9vXm

[2]: https://www.typescriptlang.org/docs/handbook/2/everyday-type...

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Re:TypeScript types can run DOOM [video] by epolanski on Thursday February 27, 2025 @02:35AM (#43192178)

Your 1 isn't equivalent to my example, line 11 is not constraining the type.

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Re:TypeScript types can run DOOM [video] by matt_kantor on Thursday February 27, 2025 @07:05AM (#43193582)

I know it's not equivalent, it was just an example to show what `any` does (and that it's more than "just a set of all possible types").

The `T extends Record<any, any>` on line 11 is a type parameter constraint though. Are you referring to something else when you say "constraining the type"?

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Re:TypeScript types can run DOOM [video] by epolanski on Thursday February 27, 2025 @12:38PM (#43196564)

It works differently based on where those anys are and what that Record<any, any> refers to due to type variance.

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Re:TypeScript types can run DOOM [video] by undebuggable on Thursday February 27, 2025 @05:26AM (#43193024)

It's a "null" and "undefined" discussion all over, but now with transpiler.

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Re:TypeScript types can run DOOM [video] by remolueoend on Wednesday February 26, 2025 @05:18PM (#43188905)

'any' has always been intended as an escape hatch, so no abuse here [1]. The type representing the set of all possible values (the top type in the type lattice) is 'unknown'.

[1] https://www.typescriptlang.org/docs/handbook/2/everyday-type...

[2] https://www.typescriptlang.org/docs/handbook/release-notes/t...

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Re:TypeScript types can run DOOM [video] by epolanski on Thursday February 27, 2025 @02:40AM (#43192207)

unknown is not equivalent to any as a type constraint: doesn't work.

https://www.totaltypescript.com/any-considered-harmful#type-...

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Re:TypeScript types can run DOOM [video] by matt_kantor on Thursday February 27, 2025 @07:27AM (#43193748)

The widest possible function type is `(...args: never) => unknown`. This is because parameters are contravariant, and `never` is the bottom type. Using that type works in the author's example[0].

I've got an issue open about TypeScript's provided `ReturnType` type which is somewhat related to this[1].

[0]: https://tsplay.dev/Wy0Ogm

[1]: https://github.com/microsoft/TypeScript/issues/55667

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