Record with a required key

Is it possible to create a record (e.g. Record<string, Struct>) which has one required key? I’m trying to get the equivalent of something like the this in TypeScript:

interface Type {
  foo: Struct;
  [key: string]: Struct;
}

I tried using an union with object and record, but that results in something like

type Type = { foo: Struct; } | Record<string, Struct>;

Which results in “type ‘string’ can’t be used to index type”-like errors elsewhere. I currently solved it by using refinement and specifying a custom type as generic parameter, but I’d like to know if there’s an easier solution to accomplish this.

[ianstormtaylor]

My guess is that you’re looking for something like:

const MyArray = array(...)

const MyObject = intersection([
  type({ requiredKey: MyArray }),
  record(string(), MyArray)
])

[Mrtenz]

That seems to work great, thanks!