code: func NewChordAsyncResult(groupTasks []*tasks.Signature, chordCallback *tasks.Signature, backend iface.Backend) *ChordAsyncResult {
  	asyncResults := make([]*AsyncResult, len(groupTasks))
  	for i, task := range groupTasks {
  		asyncResults[i] = NewAsyncResult(task, backend)
  	}
  	return &ChordAsyncResult{
  		groupAsyncResults: asyncResults,
  		chordAsyncResult:  NewAsyncResult(chordCallback, backend),
  		backend:           backend,
  	}
  }
docs: // NewChordAsyncResult creates ChordAsyncResult instance