How to define a constructor parameter type based on another parameter

[maiden grotto]

istedist#9580

Playground Link

Preview:```ts
interface Building {
floors: number
}

const building: Building = {floors: 6}

class Person {
constructor(
public building: Building,
public position: number // How to use TypeScript type annotation to
) //
...```

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[frosty shale]

I want position to be an integer from 1 to this.building.floors.

[tight plinth]

You need to change how building is declared to preserve the type, and then use recursive type to create a union of all the allowed values.

Personally I would suggest against it.

[frosty shale]

Could you give me more detailed codes? I don't quite understand.

[tight plinth]

I’m on mobile, I’ll reply later if someone else hasn’t got to it by then.

[maiden grotto]

nonspicyburrito#0

Playground Link

Preview:```ts
interface Building {
floors: number
}

type OneTo<N extends number, R extends number[] = [never]> = R['length'] extends N
? R[number] | N
: OneTo<N, [...R, R['length']]>

class Person<T extends Building> {
constructor(building: T, position: OneTo<T['floors']>) {}
...```

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[tight plinth]

Again, I would strongly recommend you to not do this.

The extra safety is not worth the cons in most cases.