code: public final Cache2kBuilder<K, V> weigher(Weigher<K,V> v) {
      config().setWeigher(new CustomizationReferenceSupplier<Weigher>(v));
      return this;
    }
docs: Set the weigher to be used to calculate the entry weight. The parameter {@link #maximumWeight(long)} needs
  to be specified as well. Using a weigher has a slightly performance impact on the update of existing entries.