Update Pick to use new key remapping in mapped types

Search Terms

pick omit key remapping

Suggestion

Update Pick in lib.d.ts to be:

type Pick<T, K extends keyof T> = {
    [P in keyof T as Extract<P, K>]: T[P];
};

It is currently defined as:

type Pick<T, K extends keyof T> = {
    [P in K]: T[P];
};

Use Cases

With this new definition, typescript can statically analyze the keys, which allows interfaces to extends these types.

Examples

interface Base {
    a: number,
    b: string,
    c: boolean,
}

// Errors: "An interface can only extend an object type or intersection of object types with statically known members"
interface PickBase0<K extends keyof Base> extends Pick<Base, K> {
    pickedKeys: K
}

type Pick1<T, K extends keyof T> = { [L in keyof T as Extract<L, K>]: T[L] }

// Works
interface PickBase1<K extends keyof Base> extends Pick1<Base, K> {
    pickedKeys: K
}

Playground Link

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

まず lib.d.ts の現在の Pick 定義を調査し、mapped types と interface extension を含むリンク先の Playground の例を再現します。提案された key-remapping の定義を既存の動作と比較します。例が既存の Pick の動作を壊さずに動作し、関連する TypeScript のチェックに合格すれば完了です。