code: public function filter(callable $condition)
      {
          $storage = [];
  
          foreach ($this->storage as $key => $value) {
              if ($condition($key, $value)) {
                  $storage[$key] = $value;
              }
          }
  
          return new static($this->keyType, $this->valType, $storage);
      }
docs: {@inheritdoc}