code: func (f *ConstraintFilter) SetTask(t *api.Task) bool {
  	if t.Spec.Placement == nil || len(t.Spec.Placement.Constraints) == 0 {
  		return false
  	}
  
  	constraints, err := constraint.Parse(t.Spec.Placement.Constraints)
  	if err != nil {
  		// constraints have been validated at controlapi
  		// if in any case it finds an error here, treat this task
  		// as constraint filter disabled.
  		return false
  	}
  	f.constraints = constraints
  	return true
  }
docs: // SetTask returns true when the filter is enable for a given task.