Overloaded indexed type isn't initializable with an object literal

[indutny-signal]

Bug Report

🔎 Search Terms

"Overloaded indexed type"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about it

⏯ Playground Link

Playground link with relevant code

💻 Code

type X = {
   [key: string]: { a: number; }
} & {
    b: { b: number};
}

let x: X = {
    a: { a: 1 },
    b: { b: 1 },
}

🙁 Actual behavior

Type error:

Type '{ a: { a: number; }; b: { b: number; }; }' is not assignable to type 'X'.
  Type '{ a: { a: number; }; b: { b: number; }; }' is not assignable to type '{ [key: string]: { a: number; }; }'.
    Property 'b' is incompatible with index signature.
      Property 'a' is missing in type '{ b: number; }' but required in type '{ a: number; }'.

🙂 Expected behavior

No type error

[jcalz]

The term "overloaded indexed type" doesn't really convey what you're doing. The behavior here is working as intended.

It looks like you're trying to write a "rest index signature" type as requested in #17867 (and mentioned in SO here), and unfortunately there's not really any great way to do it. An intersection is okay-ish to read from but you can't easily initialize it, as you can see.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.