Nominal Types in TS

nominal-types.ts

// https://www.typescriptlang.org/play#example/nominal-typing

type ValidatedInputString = string & { __brand: "User Input Post Validation" };


// https://speakerdeck.com/naoya/typescript-niyoru-graphql-batukuendokai-fa-75b3dab7-90a8-4169-a4dc-d1e7410b9dbd?slide=91

declare const __newtype: unique symbol;

export type newtype<Constructor, Type> = Type & {
  readonly [__newtype]: Constructor;
};
  
export type TagId = newtype<"TagId", string>;
  
export function TagId(value: string): TagId {
  if (validate(value)) {
    return value as TagId;
  }
  
  throw new Error(`invalid tagId=${value}`);
}