Type assertions

[m-rutter]

I've been thinking a lot about validation libaries and I share your frustration with Yup. Yup does not get everything right. I'm scared about to introducing io-ts is it has a high a cognitive overhead, but I really love what io-ts does.

I think I'll experiment with this libarary a bit, but in terms of io-ts features do you think zod could be improve with these features?

• built in type guards - i.e. io-ts's is() method on codecs.
• built in type assertions - (maybe call it assert()) using the new assertion function types in typescript 3.7 (io-ts doesn't actually have this probably because it wants us to use Either instead of exceptions)
• branded types - doing io-ts's symbol trickery to create types like NonZeroNumber or Email
  • it might be difficult to do that one while remaining ergonomic

[colinhacks]

Just implemented type guards and published it to zod 1.0.5. I'm using io-ts's same .is() API. That was an easy one :)

Tried to implement type assertions as well but it looks like it's not possible to do that yet without requiring duplicative typings :/ We'll have to wait and see on that.

I'm splitting off the feature request for branded types into a different issue 👍

[colinhacks]

For future reference, the .is() method has been replaced by .check(). .is() will still work until the release of zod@2 but it should be considered deprecated.

I'm closing this, since type assertions don't appear to work currently for generic classes such as ZodType. If this changes in the future I'll look into it again. And of course if someone cleverer than me figures out how to make assertions work, PRs are welcome!

[vlinder]

Whatever happened to .is/.check? Can we get them back? Is there another way of doing this now that I'm missing?

I'm using 3.19.1 and can't seem to find anything in the docs..

[ceefour]

https://www.npmjs.com/package/typed-assert mentions:

Consider using zod
While this library does a fine job for most simple use cases, please consider using zod if you need more complex assertions.

It doesn't seem that zod is able to perform TypeScript 3.7 assertions the way typed-assert does it.
I've tried using .parse() and the checked value is still "not asserted (at compile-time)".