Comment by shepherdjerred

6 hours ago

I love how far Java has come. I still prefer TypeScript since I do a lot of frontend work and prefer to use the same language across the stack.

With the said, you can do exhaustive pattern matching in TypeScript! https://github.com/gvergnaud/ts-pattern

8 comments

shepherdjerred

ngruhn 4 hours ago

Isn't that overkill? You can check exhaustiveness with a trivial little helper:

    function exhaustive(witness: never): never {
      return witness
    }

https://www.typescriptlang.org/play/?#code/FAFwngDgpgBAKgZQB...

whilenot-dev 3 hours ago

Agree, python calls this little helper assert_never[0]. I opened an PR to add it to the TypeScript docs some time ago: https://github.com/microsoft/TypeScript-Website/pull/3599
[0]: https://docs.python.org/3/library/typing.html#typing.assert_...
n_e 3 hours ago

In the example you don't even need the default clause and the helper (the error message without it is worse though).

ddosmax556 3 hours ago

you can just to

    default:
        matched satisfies never
        throw new Error(...)

You don't even need a function.

wk_end 4 hours ago

You don't need a library for this; the idiomatic approach is to lean on TypeScript's narrowing and native control flow (ifs and switches, or maybe IIFEs), along with (maybe) the never type to enforce exhaustiveness.

https://www.typescriptlang.org/play/?jsx=4#code/JYWwDg9gTgLg...

I guess the library is slightly nicer, arguably, but I don't think it's worth the external dependency and added complexity.

shepherdjerred 2 hours ago

I knew I should've written a disclaimer about doing this in vanilla TypeScript

Yes, you can do it via an assert never in a switch. That isn't pattern matching. That's an exhaustive switch enforced at compile time

Which is nice, but again, it's not pattern matching.