code: func flattenClusterHostGroup(d *schema.ResourceData, obj *types.ClusterHostGroup) error {
  	var hostIDs []string
  	for _, v := range obj.Host {
  		hostIDs = append(hostIDs, v.Value)
  	}
  
  	return structure.SetBatch(d, map[string]interface{}{
  		"host_system_ids": hostIDs,
  	})
  }
docs: // flattenClusterHostGroup saves a ClusterHostGroup into the supplied ResourceData.