Create a class where each method is required to be a "getter" function

Question

Create a class where each method is required to be a "getter" function

Is it feasible to establish a class in which all methods must be getters?

Possible Implementation:

class Example implements AllGetters {
  get alpha () {
  }
  get beta () {
  }
}

Not Acceptable:

class Example implements AllGetters {
  get alpha () {
  }
  beta () {
  }
}

typescript

Answer 1

Answer №1

To make it possible, you can utilize the Exclude method with a generic type:

type AllGetters<T> = {
    [k in keyof T]: Exclude<T[k], Function>
}

class A implements AllGetters<A> {
    // simple properties: OK
    a: string = 'foo';
    b: number = 1;

    // type error: type '() => number' is not assignable to type 'never'.
    c(): number {
        return 2;
    }

    // getter: OK
    get d(): string {
        return 'hi';
    }

    // getter: not OK because it returns a function
    // type error: type 'Function' is not assignable to type 'never'.
    get e(): Function {
        return console.log;
    }
}

Points to consider:

There is no distinction in type between a simple property and a getter; as long as all actions are getters, it should meet your criteria.
A getter that returns a function is also not permitted, as there is no difference in type from a method.

Playground Link

Answer 2

To make it possible, you can utilize the Exclude method with a generic type:

type AllGetters<T> = {
    [k in keyof T]: Exclude<T[k], Function>
}

class A implements AllGetters<A> {
    // simple properties: OK
    a: string = 'foo';
    b: number = 1;

    // type error: type '() => number' is not assignable to type 'never'.
    c(): number {
        return 2;
    }

    // getter: OK
    get d(): string {
        return 'hi';
    }

    // getter: not OK because it returns a function
    // type error: type 'Function' is not assignable to type 'never'.
    get e(): Function {
        return console.log;
    }
}

Points to consider:

There is no distinction in type between a simple property and a getter; as long as all actions are getters, it should meet your criteria.
A getter that returns a function is also not permitted, as there is no difference in type from a method.

Playground Link

Create a class where each method is required to be a "getter" function

Answer №1

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