I'm trying to make a Record of this shape where the id property equals the key of each object entry:

{
  id_1: {
     id: 'id_1',
     date: 1234
     comment: 'blah'
  },
  id_2: {
     id: 'id_2',
     date: 5678,
     comment: 'boo'
  }
}

Here's what I've come up with so far:

export type TMap<T extends string> = {
  [P in T]: { _id: P; date: number; comment: string };
};

However, when I use it I need to pass in a paremeter like this:

const myMap: TMap<string> = {...}

Is the a simpler way to achieve a record where the key is equal to one of the value's properties?

CodePudding user response：

I'm not sure if it's possible to get the compiler to infer what you want using just an annotation without generics, but you could use a functional approach:

TS Playground link

function validMap <T extends {
  [K in keyof T]: K extends string ? {
    id: K;
    date: number;
    comment: string;
  } : never;
}> (value: T): T {
  return value;
}

const map1 = validMap({
  a: {
    id: 'a',
    date: 1,
    comment: 'hello',
  },
  b: {
    id: 'b',
    date: 2,
    comment: 'world',
  },
});

const map2 = validMap({
  a: {
    id: 'a',
    date: 1,
    comment: 'hello',
  },
  b: {
    id: 'a',
//  ^^
// Type '"a"' is not assignable to type '"b"'.(2322)
    date: 1,
    comment: 'hello',
  },
});

CodePudding user response：

You could specify string as the default type of your TMap:

export type TMap<T extends string = string> = {
  [P in T]: { id: P; date: number; comment: string };
};

Then you could use it like so:

const myMap: TMap = { ... }