Hello all,

I use Delphi style of programing in Lazarus to keep a compatibility with Kylix and therefore I want to get this code which is valid of Freepascal's ObjectPascal, but in {$MODE Delphi} it doesn't accept calling of "MyItems[index]" and writes "Array type required".

How to adapt this code to be valid for Delphi mode.

TYPE
  PtrUInt = DWord;
  TMyObj  = PtrUInt;
  PMyObj  = ^TMyObj;
  TArr    = ARRAY OF TMyObj;
procedure TForm1.FormCreate(Sender: TObject);
VAR MyItems         :PMyObj;
    Arr             :TArr;
begin
  SetLength (Arr, 5);
  Arr[0] := 1;
  Arr[1] := 2;
  Arr[2] := 3;
  Arr[3] := 4;
  Arr[4] := 5;
  MyItems := Pointer (Arr);
  ShowMessage (IntToStr (MyItems[0]));
end;

Thanks.

Since you posted an incomplete sample, I can only guess, but...

ShowMessage (IntToStr (MyItems[0]));

I think this should work:
   ShowMessage (IntToStr (MyItems[0]()));

Please also file a bug report with a compilable example (which does not depend on Lazarus) that demonstrates the problem, although some things have been fixed recently regarding procvars in Delphi mode and it may already work with svn trunk.

Jonas

Well, at least if the original code compiles with Delphi/Kylix.

Jonas

<<< 19.01.2010 11:39 - Jonas Maebe "" >>>

JM> Well, at least if the original code compiles with Delphi/Kylix.

Thank Jonas for you reply, but FreePascal and Kylix as well reports the same error.

It should not compile in Delphi mode.
Array syntax is not supported by Delphi.

So there is no bug.

Michael.

Michael Van Canneyt wrote

It should not compile in Delphi mode. Array syntax is not supported by Delphi.

Oops, only now I see he was trying to index a pointer like an array. And even in FPC I would very strongly recommend against typecasting a dynamic array to a pointer and then performing operations using this pointer. Dynamic arrays are opaque structures and trying to directly access the underlying data should never be done.

Jonas

<<< 19.01.2010 13:10 - Jonas Maebe "" >>>

Michael Van Canneyt wrote

> It should not compile in Delphi mode. > Array syntax is not supported by Delphi.

JM> Oops, only now I see he was trying to index a pointer like an array. JM> And even in FPC I would very strongly recommend against typecasting a JM> dynamic array to a pointer and then performing operations using this JM> pointer. Dynamic arrays are opaque structures and trying to directly JM> access the underlying data should never be done.

Hello Jonas,

But this ways is already used in LCL/FPC source as well.

I don't know about the LCL, but I guess in the FPC sources the only place where this is done is inside the RTL helpers that are used to manage the dynamic arrays. These by definition depend on the internal layout of the dynamic array and will be updated if something would change about dynamic arrays.

I also don't see any advantage to using a pointer instead of a dynamic array directly. It will not be faster in any way, since there are no uniqueness checks for dynamic arrays. In fact, it will probably be slower, since you now have two variables in use: one to hold a reference to the dynamic array, and one for the extra pointer.

Jonas

In our previous episode, Jonas Maebe said:

Hmm, under delphi at least, it is cheaper to do

var pstart,pend : PSomeType;
if length(sometypedynarray)>0 then
  begin
    ;
    peind (sometypedynarray)-1];
    while (pstart<=peind) do
      begin
        operate_on(pstart);
        inc(pstart);
      end;
  end;

then for i over a dynarray, even if sometype is a simple type.

I can't imagine why that would be any faster than a simple for-loop, except for an implementation detail in the code generator or optimiser of the tested Delphi version(s) (or in case range checking is enabled -- but in that case using pointers to work around range checking would be strange). And it most certainly looks a lot worse than

for i:=0 to high(sometypedynarray) do
   operate_on(sometypedynarray[i]);

It would also surprise me if any speed difference that may exist were significant.

Jonas