Function derived

packages/state/src/decorators.ts:29–46

(
  target: (this: This) => Return,
  _: ClassGetterDecoratorContext<This, Return>
)

}

export function derived<This, Return>(
  target: (this: This) => Return,
  _: ClassGetterDecoratorContext<This, Return>
) {
  const map: WeakMap<any, Signal<Return>> = new WeakMap();

  return function (this: This): Return {
    let result = map.get(this);

    if (!result) {
      result = computed(target.bind(this));

      map.set(this, result);
    }

    return result.value;
  };
}

/**
 * Make a field enumerable (or non‑enumerable) on every instance.