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Comment by jrimbault | Hacker News Reader

I'd really like something like a compiler step/plugin to generate the validators from the declared typescript types.

You can generate JSON Schema from TS with this library: https://github.com/YousefED/typescript-json-schema

It's certainly conceivable to build an equivalent for Zod but you'll eventually want to validate types that aren't expressible in TS (i.e. Integer).

This looks like it generates JSON Schema, but not runtime validators?

For that you could use something like ajv. Json schema has the advantage of being usable across different languages, but it does come with the overhead of maintaining those files and keeping it in sync with your other repos.

This is basically that but in the opposite direction. It also has the advantage of being able to express validations that you can't express in the type system.

Do you have an example of the kind of validation couldn't be expressed in the type system?

Min or max length of an input. Any type of string validation like email or something similar that's validated via regex.

root_axis gave some good examples. Also types like `int` or `decimal` (which you can also pair with branded static types, but they don't actually guarantee anything other than their name. Really any kind of refinement you can imagine on primitive types.

I should point out that there's nothing in Zod (yet) that isn't expressible in Typescript. I'll eventually get around to doing string/numerical validations (`.isEmail()`, etc) that go beyond TS but currently all functionality has an equivalent in TS.

Yeah, that's really something that feels like it should be a part of the language, because it would be so useful!

It's explicitly one of the language's non-goals[1].

> Add or rely on run-time type information in programs, or emit different code based on the results of the type system. Instead, encourage programming patterns that do not require run-time metadata.

[1] https://github.com/Microsoft/TypeScript/wiki/TypeScript-Desi...

I understand it (there's already enough to do at type level that runtime level is a non-goal), but types are purely indicative at IO boundaries. Validation still needs to happen

That's right. So since it won't be a part of the language, libraries like this are being developed.

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