TS2538: Type 'unique symbol' cannot be used as an index type

Question

I have this:

const symbols = {
   typeMap: Symbol('type.map')
}

interface LangMap {
  [key: string]: string | true,
  golang: string,
  typescript: string,
  java: string,
  swift: string
}

export const setTypeMap = function(v: LangMap) : LangMap{
  v[symbols.typeMap] = true;
  return v;
};

I get this error:

TS2538: Type 'unique symbol' cannot be used as an index type.

Does anyone know what that error is about? I am on tsc version 3.1.6.

Aynat

[key: string]? – Raymond

I tried this [key: string | symbol] didn't work either – Aynat

Unfortunately this issue appears to still be outstanding (I was actually led here by your comment on GitHub). I've just pinged some TS maintainers to see if there's anything that can be done. – Pteridology

Does anybody have an update on this ? – Cardoso

github.com/microsoft/TypeScript/issues/1863 @Cardoso – Quintet

Answer 1

This works:

type SymbolObject<T extends object = Record<any,any>, K = T[keyof T]> = {
[key:string|number|symbol]:K
}
// it would be advised to have true type definitions here, but that's annoying.
const bar:SymbolObject = {};
const foo = Symbol("foo");
bar[foo] = "hello!"

Syriac

Answer 2

My poor workaround :

const bar: Record<any, string> = {};
const FOO = Symbol('foo');

// eslint-disable-next-line @typescript-eslint/no-explicit-any
bar[FOO as any] = 'sad';

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