Make sure the subset interface is selected from the interface / Choose PickDeep<>?

Question

Make sure the subset interface is selected from the interface / Choose PickDeep<>?

I am searching for a solution using the following interface:

interface Person {
  age: number,
  name: string,
  hometown?: {
    city: string,
    zip: number
  }
}

type SubPerson = EnsureSubInterface<Person, {
  name: string
}>

an example that would be accepted:

const x: SubPerson {
  name: "Tom"
}

an example that would be rejected:

const x: SubPerson {
  age: 12
}

typescript

Answer 1

Answer №1

If the goal is to ensure that the second type parameter is a subset of the original at any given level, you can implement this using DeepPartial as a constraint on the second parameter for EnsureSubInterface

type DeepPartial<T> = {
    [P in keyof T]?: T[P] extends Array<infer U>
    ? Array<DeepPartial<U>>
    : T[P] extends ReadonlyArray<infer U>
        ? ReadonlyArray<DeepPartial<U>>
        : DeepPartial<T[P]>
};

type EnsureSubInterface<T, U extends DeepPartial<T>> = U

interface Person {
    age: number,
    name: string,
    hometown?: {
        city: string,
        zip: number
    }
}

type SubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        city: string,
    }
}>


type NotSubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        city: number, // error
    }
}>


type NotSubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        City: string, // error
    }
}>

Depending on your tslint config you might want to make these modifications:

type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends (infer U)[]
  ? DeepPartial<U>[]
  : T[P] extends ReadonlyArray<infer U>
      ? ReadonlyArray<DeepPartial<U>>
      : DeepPartial<T[P]>
};

Answer 2

If the goal is to ensure that the second type parameter is a subset of the original at any given level, you can implement this using DeepPartial as a constraint on the second parameter for EnsureSubInterface

type DeepPartial<T> = {
    [P in keyof T]?: T[P] extends Array<infer U>
    ? Array<DeepPartial<U>>
    : T[P] extends ReadonlyArray<infer U>
        ? ReadonlyArray<DeepPartial<U>>
        : DeepPartial<T[P]>
};

type EnsureSubInterface<T, U extends DeepPartial<T>> = U

interface Person {
    age: number,
    name: string,
    hometown?: {
        city: string,
        zip: number
    }
}

type SubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        city: string,
    }
}>


type NotSubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        city: number, // error
    }
}>


type NotSubPerson = EnsureSubInterface<Person, {
    name: string,
    hometown: {
        City: string, // error
    }
}>

Depending on your tslint config you might want to make these modifications:

type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends (infer U)[]
  ? DeepPartial<U>[]
  : T[P] extends ReadonlyArray<infer U>
      ? ReadonlyArray<DeepPartial<U>>
      : DeepPartial<T[P]>
};

Make sure the subset interface is selected from the interface / Choose PickDeep<>?

Answer №1

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