code: private function equalComparison(UnitCandidate $a, UnitCandidate $b, $property, $quantity)
      {
          if ($a->{$property} == $quantity && $b->{$property} != $quantity) {
              return -1;
          }
          if ($a->{$property} != $quantity && $b->{$property} == $quantity) {
              return 1;
          }
  
          return false;
      }
docs: Returns -1 if A's equals quantity but not B.
  Returns 1 if B's equals quantity but not A.
  Else returns false.
  
  @param UnitCandidate $a
  @param UnitCandidate $b
  @param string        $property
  @param float         $quantity
  
  @return bool|int