Add a new type PublicOf

[sroucheray]

Suggestion

Add the PublicOf type suggested in this issue's comment by @DanielRosenwasser

Use Cases

Implement a class public properties/methods without the need to implement private/protected ones.

Examples

// type to add
type PublicOf<T> = {
    [P in keyof T]: T[P]
}

// use case
class C {
    private foo();

    public bar();
}

// No need to implement private method foo !
class D implements PublicOf<C> {
    public bar() {}
}

Checklist

My suggestion meets these guidelines:

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

[dragomirtitian]

This seems to me a marginal improvement over Pick<C, keyof C>

declare class C {
    private foo(): void

    public bar(): void
}

// No need to implement private method foo !
class D implements Pick<C, keyof C> {
    public bar() { }
}

[sroucheray]

Good point, alternate implementation:

type PublicOf<T> = Pick<T, keyof T>;

[sroucheray]

I'm trying a contribution, I'm not sure that my pull request #31970 is valid but I'm still trying.