asked on

Storing a record in a TList with different struct

Hello,

What is the best way to identify wich kind of record is in the list?

Example

type
TSomethingA = record //A = ANSI
chBla: array [0..9] of AnsiChar;
end;
PSomethingA = ^TSomethingA;

TSomethingW = record //W = UNICODE
chBla: array [0..9] of WideChar;
end;
PSomethingW = ^TSomethingW;

//global var
var
lsList: TList;

//the lsList is created and inside has a lot of PSomethingW and PSomethingA stored
procedure Something;
var
SomethingA: PSomethingA;
SomethingW: PSomethingW;
i: Integer;
begin
//now, walking in lsList, an item can be of type SomethingA or SomethingW
for i := 0 to Pred(lsList.Count) do
//what is the best method to identify, if the current item "lsList[ i ]" is a SomethingA or SomethingW?
end;
end;

Emmanuel PASQUIER

you can't with records, or it would require a complex set of records declarations that would follow a simple rule : having a Type field before (integer)

Easiest way : use class instead

type
  TSomethingA = Class //A = ANSI
    chBla: array [0..9] of AnsiChar;
  end;
//  PSomethingA = ^TSomethingA;

  TSomethingW = Class //W = UNICODE
    chBla: array [0..9] of WideChar;
  end;
//  PSomethingW = ^TSomethingW;

//global var
var
  lsList: TObjectList; // Change TList to TObjectList

//the lsList is created and inside has a lot of PSomethingW and PSomethingA stored
procedure Something;
var
  SomethingA: TSomethingA;
  SomethingW: TSomethingW;
  i: Integer;
begin
  //now, walking in lsList, an item can be of type SomethingA or SomethingW
  for i := 0 to Pred(lsList.Count) do
   if lsList[ i ] is TSomethingA Then // Use Is operator on TObject
    begin
...
    end;
end;

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cebasso

ASKER

hey epasquier!

cool!
but, the struct has more members like

chBla: array [0.9] of WideChar;
dwFlags: DWORD;
iSomething: Integer;
//and more

no problem?

and actually i'm using New() to store in TList, like

var
SomethingA: PSomethingA;
begin
New(SomethingA);
FillChar(SomethingA^, SizeOf(TSomethingA), 0);
//fill members
lsList.Add(SomethingA);
Dispose(SomethingA);
end;

now, with your code, i need just to change PSomethingA to TSomethingA as a class, do the same and store in a TObjectList instead TList like your example?

Emmanuel PASQUIER

no, you can't create objects with New, and do not use FillChar on them.
It's possible that your needs are not compatible with Objects... So you might have to do it the hard way, with a Type field in records.
I wont have time to explain you that alternate today, I'll think of the best thing for you and explain monday

ASKER CERTIFIED SOLUTION

Emmanuel PASQUIER

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GeneralTackett

How about using records with variant parts example:
TPerson = record
FirstName : string[40];
LastName : string[40];
{ Fixed portion of record begins here }
BirthDate: TDate;
case
Citizen: Boolean of
{ variant portion of record begins here }
True: (BirthPlace: string[40]);
False:
(
Country: string[20];
EntryPort: string[20];
EntryDate: TDate;
ExitDate: TDate
);
end;

cebasso

ASKER

Thanks!