The is my code.

type t = 'a' | 'b' | 'c';

const objs = {
  obj1: { a: 1 },
  obj2: { a: 1, b: 2 },
};

// inferred type is { a: number }
objs.obj1.c; // Error

I want to constrain the value of objs to have keys belonging to t. So I rewrite it as below:

type t = 'a' | 'b' | 'c';
type SubsetOfT = Partial<Record<t, number>>;

const objs: Record<string, SubsetOfT> = {
  obj1: { a: 1 },
  obj2: { a: 1, b: 2 },
};

// inferred type is {a?: number; b?: number; c?: number}
objs.obj1.c; // number | undefined

Then I lost the specific type information.

type t = 'a' | 'b' | 'c';


function constrainKeys<T extends Record<string, Partial<Record<t, number>>>>(obj: T): T {
  return obj;
}

const objs = constrainKeys({
  obj1: { a: 1 },
  obj2: { a: 1, b: 2 }
});

// inferred type is { a: number }, that's good
objs.obj1.c = 1; // Error

This code is exactly what I want. It can correctly infer the type of the value of obj1 as {a: number;} instead of {a?: number; b?: number; c?: number}. But is there a more concise way to write it? The constrainKeys function reduces readability. I asked GPT, but it couldn’t answer