Method reset

src/butil/containers/optional.h:377–382

Destroys any contained value if the `optional` is not empty.

    // Destroys any contained value if the `optional` is not empty.
    void reset() {
        if (_engaged) {
            _storage.Destroy();
            _engaged = false;
        }
    }

    // Constructs the contained value in-place.
    // Return a reference to the new contained value.