extracting redux-like actions from type.enumerated discriminated union

Trying unsuccessfully to convert some redux/reducer-like "action" object types to arktype:

type TestAction1 = { type: 'ACTION_1', value: number }
type TestAction2 = { type: 'ACTION_2', name: string}
type TestAction = TestAction1 | TestAction2

function CreateTestAction1(): Extract<TestAction, {type: 'ACTION_1'}> {
    return { type: 'ACTION_1', value: 3 }
}

const testAction1 = CreateTestAction1() // type === TestAction1

type TestAction1 = { type: 'ACTION_1', value: number }
type TestAction2 = { type: 'ACTION_2', name: string}
type TestAction = TestAction1 | TestAction2

function CreateTestAction1(): Extract<TestAction, {type: 'ACTION_1'}> {
    return { type: 'ACTION_1', value: 3 }
}

const testAction1 = CreateTestAction1() // type === TestAction1

Below is how I did the conversion. The Extract on the type.enumerated results in a never and I don't follow why.

const ArkAction1 = type({ type: type.unit("ACTION_1"), value: type.number })
const ArkAction2 = type({ type: type.unit("ACTION_2"), name: type.string })
const ArkAction = type.enumerated(ArkAction1, ArkAction2)
type ArkAction = type.infer<typeof ArkAction>

function CreateArkAction1(): Extract<ArkAction, { type: 'ACTION_1'}>  {
    return { type: 'ACTION_1', value: 3 } // type not assignable to never
}

const ArkAction1 = type({ type: type.unit("ACTION_1"), value: type.number })
const ArkAction2 = type({ type: type.unit("ACTION_2"), name: type.string })
const ArkAction = type.enumerated(ArkAction1, ArkAction2)
type ArkAction = type.infer<typeof ArkAction>

function CreateArkAction1(): Extract<ArkAction, { type: 'ACTION_1'}>  {
    return { type: 'ACTION_1', value: 3 } // type not assignable to never
}

If I define the action union type in vanilla TS (from the ark inferred types) the extract works as expected:

type ArkAction1 = type.infer<typeof ArkAction1>
type ArkAction2 = type.infer<typeof ArkAction2>
type ArkAction = ArkAction1 | ArkAction2

type ArkAction1 = type.infer<typeof ArkAction1>
type ArkAction2 = type.infer<typeof ArkAction2>
type ArkAction = ArkAction1 | ArkAction2

Am I holding it wrong?

45 Replies

Dimava•2w ago

Enumerated is array.includes, not a union You need A1.or(A2) Lemme actual rewrite your code

errata•2w ago

are you sure? because when I look at the resulting type of the infer on the type.enumerated type ArkAction = type.infer<typeof ArkAction> it looks like this:

type ArkAction = Type<{ type: 'ACTION_1'; value: number }, {}> | Type<{ name: string; type: 'ACTION_2' }, {}>

type ArkAction = Type<{ type: 'ACTION_1'; value: number }, {}> | Type<{ name: string; type: 'ACTION_2' }, {}>

https://github.com/arktypeio/arktype/blob/da2f08d559e7c9a8e95ca513227a1496f9be3041/ark/type/__tests__/type.test.ts#L126-L130

errata•2w ago

Dimava•2w ago

import { type } from 'arktype'

const ArkAction1 = type({ type: "'ACTION_1'", value: 'number' })
const ArkAction2 = type({ type: "'ACTION_2'", name: 'string ' })
const ArkAction = ArkAction1.or(ArkAction2)
type ArkAction = typeof ArkAction.infer

function CreateArkAction1(): Extract<ArkAction, { type: 'ACTION_1' }> {
  return { type: 'ACTION_1', value: 3 } 
}

import { type } from 'arktype'

const ArkAction1 = type({ type: "'ACTION_1'", value: 'number' })
const ArkAction2 = type({ type: "'ACTION_2'", name: 'string ' })
const ArkAction = ArkAction1.or(ArkAction2)
type ArkAction = typeof ArkAction.infer

function CreateArkAction1(): Extract<ArkAction, { type: 'ACTION_1' }> {
  return { type: 'ACTION_1', value: 3 } 
}

errata•2w ago

hm, it does work

Dimava•2w ago

It's for const typeValue = type(['===', 'ACTION_1', 'ACTION_2']) i.e. for enums

errata•2w ago

yeah i basically have an enum though, right?

Dimava•2w ago

No A enum of let a = {}, b = [] is [a, b].includes(v), not [{}, []].includes(v) as different object instances are not equal

errata•2w ago

ahh ahhh right === ok got it

Dimava•2w ago

So you are checking if your object is one of two ArkType instances lol

errata•2w ago

ahhh ok ok, thank you that makes sense

Dimava•2w ago

BTW how do you think it should be named? The make union one and the make array of values one? I do not feel like it's named perfectly so what would you guess they are named if you never used ArkType? May be more then one variant May be inspired by other validators

errata•2w ago

enumerated is ok, that's actually how I assumed it worked previously and .or is fine as well totally though I'm not keen on the chaining

Dimava•2w ago

@ssalbdivad we need type.oneOf or type.discriminatedUnion equivalent as I expect peoples to want a way to avoid .or chaining

errata•2w ago

type.union?

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extracting redux-like actions from type.enumerated discriminated union