How to access generic type property in dynamic interface

Question

I would like to access dynamic T property in an interface to extend his typing to allow this kind of generic function:

type AnotherType<T extends {}> = T & {
    prop: boolean;
    prop2: string;
};

interface SpecialInterface<T> {
    someProperty: AnotherType<{T["someProperty"]}>; // I know what key of T I want to extends but can't understand how
}

const func = <T extends SpecialInterface<T>>(prop: T) => {
    const a = prop.someProperty.prop; // I would like no error on this
    // somethings
}

I use this for now, it works but I don't like the any typing allowing everything on the function prop:

interface SpecialInterface<T> {
    someProperty: AnotherType<{[key: string]: any}>;
}

Example of prop send to func :

interface IProp {
    someProperty: AnotherType<{prop3: number}>
}

const prop: IProp = {
    someProperty: {
        prop: true,
        prop2: "test",
        prop3 : 5
    }
}

Any ideas?

Answer 1

I hope it helps you

interface Another {
    key: number;
    value: string;
}

interface ExtraAnother extends Another {
    someProperty: number;
}

interface SpecialInterface<T extends Another> {
    someProperty: T
};

const func = (prop: SpecialInterface<ExtraAnother>) => {
    const a = prop.someProperty; // I would like no error on this
    // somethings
};

Answer 2

You can add a generic constraint T extends Record<"someProperty", any> to ensure, that T has property someProperty ( Record is a built-in type).

//                           v  add this constraint
interface SpecialInterface<T extends Record<"someProperty", any>> {
    someProperty: AnotherType<T["someProperty"]> // works
}

const func = <T extends SpecialInterface<T>>(prop: T) => {
    const a = prop.someProperty.prop; // works
}

Sample