TS: Optionals

index.ts

class Optional<T> {
  private val: T;
  private is_none: boolean;

  private constructor(value: T, is_none: boolean = false) {
    this.val = value;
    this.is_none = is_none;
  }

  static none<U>(): Optional<U> {
    return new Optional(undefined, true);
  }

  static some<T>(value: T) {
    return new Optional(value);
  }

  map<U>(handler: (obj: T) => U): Optional<U> {
    if (!this.is_none) {
      return Optional.none();
    }
    return Optional.some(handler(this.val));
  }
}

let value = Optional.some("Hello");

let thing = value.map((string) => {
  return string + string;
});