exhaustiveCheck.ts

/**
 * Represents an error when an unreachable variant is encountered at runtime
 */
export class ExhaustiveCheckError<T> extends TypeError {
  public instance: T;

  public readonly isUnexpected = true;

  constructor(msg: string, instance: T) {
    super(msg);
    this.instance = instance;
  }
}

/**
 * Force an exhaustive check in preceding control flow (e.g. `switch` blocks)
 *
 * See: https://stackoverflow.com/a/39419171
 */
export function assertExhaustiveCheck(x: never): never {
  throw new ExhaustiveCheckError('Variation unhandled', x);
}