Question

Can it be known in general whether or not placing a case within a for loop will result in bad assembly. I’m interested mainly in Delphi, but this is an interesting programming question, both in terms of style and performance.

Here are my codez!

   case ResultList.CompareType of   TextCompareType:     begin       LastGoodIndex := -1;       for I := 1 to ResultList.Count -1 do       if (LastGoodIndex = -1) and (not ResultList[I].Indeterminate) then         LastGoodIndex := I       else if not ResultList[I].Indeterminate then       begin         if (StrComp(ResultList[LastGoodIndex].ResultAsText,                      ResultList[I].ResultAsText) > 0)             and (Result  FalseEval) then           Result := TrueEval         else           Result := FalseEval;          LastGoodIndex := I;       end;     end;   end;   NumericCompareType:   begin     //Same as above with a numeric comparison   end;   DateCompareType:   begin     //Same as above with a date comparison   end;   BooleanCompareType:   begin     //Same as above with a boolean comparison   end; 

alternatively I could write

     begin       LastGoodIndex := -1;       for I := 1 to ResultList.Count -1 do       if (LastGoodIndex = -1) and (not ResultList[I].Indeterminate) then         LastGoodIndex := I       else if not ResultList[I].Indeterminate then       begin       case ResultList.CompareType of       TextCompareType:       begin          if (StrComp(ResultList[LastGoodIndex].ResultAsText,                      ResultList[I].ResultAsText) > 0)             and (Result  FalseEval) then            Result := TrueEval          else            Result := FalseEval;          LastGoodIndex := I;       end;       NumericCompareType:       begin        //Same as above with a numeric comparison       end;       DateCompareType:       begin        //Same as above with a date comparison       end;      BooleanCompareType:      begin        //Same as above with a boolean comparison      end;     end;   end;  end; 

I don’t like the second way because I’m asking a question I know the answer to in a for loop and I don’t like the first way because I’m repeating the code I use to figure out which of my objects contain valid information.

Perhaps there is a design pattern someone could suggest that would circumvent this all together.

Answer 1

Why not using subclasses?

This saves the use of the case statement.

TComparer = class  protected   function Compare(const AItem1, AItem2: TItem): Boolean; virtual; abstract; public   procedure DoCompare(ResultList: ...); end;  TTextComparer = class (TComparer) protected   function Compare(const AItem1, AItem2: TItem): Boolean; override; end;  procedure TComparer.DoCompare(ResultList: ...); var   LastGoodIndex, I : Integer; begin    LastGoodIndex := -1;   for I := 1 to ResultList.Count -1 do   if (LastGoodIndex = -1) and (not ResultList[I].Indeterminate) then     LastGoodIndex := I   else if not ResultList[I].Indeterminate then begin     if Compare(ResultList[LastGoodIndex], ResultList[I]) then       Result := TrueEval     else        Result := FalseEval;   end; end;  function TTextComparer.Compare(const AItem1, AItem2: TItem): Boolean;  begin   Result := StrComp(ResultList[LastGoodIndex].ResultAsText,     ResultList[I].ResultAsText) > 0)     end;