Is there a way to dynamically generate members in a TypeScript definition?

Question

I don't think the title for this question is very good, but I had trouble coming up with something better, so it'll do for now.

I'm also fairly sure that what I want isn't supported, but I'd love to be proved wrong!

I have an API I'm calling, and it varies the member names in the object returned based on the query.

eg

GetInfo(languages?:string[]);
GetInfo() => { name: "Cologne" };
GetInfo(["en", "de"]) => { name: "Cologne", name_en: "Cologne", name_de: "Köln" };

Is there a way to create a definition that will "generate" the name_{language} members?

Answer 1

There is no support for manipulation of property names in this way (ie. concatenate a string to another string and have this be a type checked property).

The best you can do is not just return an object with the properties being the same name as the language names:

function GetInfo<T extends string>(langs: T[]): Record<T | 'default', string>{
  return null as any;
}
let values = GetInfo(["en", "de"]) // values is  { en: string; de: string; default: string  }
values.default
values.de
values.en

There is an issue on GitHub that suggest adding support for string literal manipulations, but it's nowhere on the roadmap for now