I need to create a Typescript Record with the keys defined in an independent type and specific types for each value.

The keys are defined as follows:

// Keys must be available/iterable at runtime
const keys = ['a', 'b', 'c'] as const
export type Key = typeof keys[number]

Now I see two options, both flawed.

Option 1: repeat the keys and define the value types explicitly, as needed. Flaw: Structure isn't actually based on Key and they might deviate.

export type Structure1 = {
  a: number
  b: boolean
  c: string
}

Option 2: define a record from Key and lose the specific type information on the values:

export type Structure2 = Record<Key, number | boolean | string>

Is there a third option for a Structure3 that uses Key as the key type and an explicit value type per key?

CodePudding user response：

You can keep it DRY and enforce your interface keys like this (performance bonus: no extra runtime code):

TS Playground link

type EnforceKeys<Key extends string, T extends Record<Key, unknown>> = {
  [K in keyof T as K extends Key ? K : never]: T[K];
};

const keys = ['a', 'b', 'c'] as const;
type Key = typeof keys[number];

// Ok
type Structure1 = EnforceKeys<Key, {
  a: number;
  b: boolean;
  c: string;
}>;

// Ok, and extra properties are omitted
type Structure2 = EnforceKeys<Key, {
  a: number;
  b: boolean;
  c: string;
  d: number[]; // omitted from type
  e: boolean; // omitted from type
}>;

// Error: Property 'c' is missing in type... (2344)
type Structure3 = EnforceKeys<Key, {
  a: number;
  b: boolean;
}>;