TS branded string as key of the object

问题

Imagine, that I have class Foo with string identifier.

class Foo {
    id = '123' as FooId;
}

I try to ensure static typing of it using a brand enum.

enum FooIdBranding {}
type FooId = string & FooIdBranding;

So now, my goal is specific object, where the key is FooId and the value is Foo.

type fooCache = { [key: FooId]: Foo };

Unfortunately, it doesn't work:

TS1023: An index signature parameter type must be 'string' or 'number'

I thought, that the Record is my solution, but is doesn't work too.

type FooCache = Record<FooId, Foo>;

({} as FooCache)['123' as FooId] = new Foo();

TS 7017: Element implicitly has an 'any' type because type Record<FooId, Foo> has no index signature

Is there a correct way in TypeScript to resolve this problem?

来源：https://stackoverflow.com/questions/56020400/ts-branded-string-as-key-of-the-object