`c.req.query` should support generics

[kahosan]

What is the feature you are proposing?

Hey

Currently, the type of query is Record<string, string>. However, when I have a predefined type, such as:

interface A {
  userId: string
  type: 'all' | 'post'
}

I hope the type of query can be changed to A, so that I can directly use c.req.query<A>() to pass parameters to functions that accept type A.

Perhaps its type definition is like this:

query<T = Record<string, string | undefined>>(): T

[yusukebe]

Hi @kahosan,

This seems to be a good suggestion. However, inferring types perfectly is difficult for me, or it might be impossible.

For example, this issue

I'll continue to investigate it. Thanks.

[kahosan]

right, I gave it a try.

When string exists, literals will be directly inferred as string instead of the designated literal type. Moreover, different keys with distinct literal types will be merged.

For example:

type T = {
  a: 'a'
  b: 'b'
}

const type = query<T>('a')
//    ^? type: 'a' | 'b'

type T = {
  a: string
  b: 'b'
}

const type = query<T>('a')
//    ^? type: string

This seems to be a problem with TypeScript, do we have a way to infer the type of key?

[yusukebe]

This seems to be a problem with TypeScript, do we have a way to infer the type of key?

Hmm. I'll keep to investigating it, but it may be impossible for TypeScript (TypeScript is sometime troublesome).