code: func expandClusterHostGroup(d *schema.ResourceData, name string) (*types.ClusterHostGroup, error) {
  	obj := &types.ClusterHostGroup{
  		ClusterGroupInfo: types.ClusterGroupInfo{
  			Name:        name,
  			UserCreated: structure.BoolPtr(true),
  		},
  		Host: structure.SliceInterfacesToManagedObjectReferences(d.Get("host_system_ids").(*schema.Set).List(), "HostSystem"),
  	}
  	return obj, nil
  }
docs: // expandClusterHostGroup reads certain ResourceData keys and returns a
  // ClusterHostGroup.