Union type as key in interface?

Question

Is it possible to use a union type as a key in an interface? For example, I want to do something like this:

interface IMargin {   [key in 'foo' | 'bar']: boolean; } 

But I'm getting this error:

A computed property name in an interface must refer to an expression whose type is a literal type or a 'unique symbol' type.ts(1169)

Is there any way around this?

The use case is turning an array of values into an interface:

const possibleTypes = ['foo', 'bar']; interface Types {     foo?: boolean;     bar?: boolean; } 

Answer 1

You can use an object type instead of an interface, which are mostly interchangeable:

type IMargin = {     [key in 'foo' | 'bar']: boolean; } 

Answer 2

This is not necessarily an answer, but I think this may interest others.

You can use a Union Type as a key in a sub-property of an Interface.

export type Language = 'EN' | 'DE' | 'IT';  export interface Document {   generic: string;   languages: {     [key in Language]: string[];   } }