option.ts

class Option<T> {
  private readonly value?: T;

  constructor(value?: T) {
    this.value = value;
  }

  public isSome() {
    return this.value !== void 0;
  }

  public isNone() {
    return this.value === void 0;
  }

  public unwrap() {
    if (this.value === void 0) {
      throw new Error('unwrapped none option');
    }
    return this.value;
  }

  public unwrapOr(def: T) {
    return this.value === void 0 ? def : this.value;
  }

  public unwrapOrElse(f: () => T) {
    return this.value === void 0 ? f() : this.value;
  }

  public map<U>(f: (v: T) => U): Option<U> {
    if (this.value === void 0) {
      return this as unknown as Option<U>;
    }
    return new Option(f(this.value));
  }

  public mapOr<U>(def: U, f: (v: T) => U): U {
    return this.value === void 0 ? def : f(this.value);
  }
}

export const some = <T>(value: T) => new Option(value);
export const none = () => new Option();