How exactly are instantiated classes treated in an array? Can I copy one into another? And if I unallocate an array member, does it automatically Destroy the object?

I have objects stored in a dynamic array, and I want to delete an arbitrary record. What I have right now is:

var
   index,
   last : integer;
begin
   last := length (t_volumes) - 1;
   index := 0;
   while ((t_volumes [index]  t_current_volume) and (index < last)) do
       inc (index);
   if (t_current_volume = t_volumes [index]) then
     t_volumes [index].Destroy;
   SetLength (t_volumes, last);
end;

This produces bad results, as it currently sits. What am I doing wrong?

Here's the code I *actually* have in the method:

var
   index,
   last : integer;
begin
   last := length (t_volumes) - 1;
   index := 0;
   while ((t_volumes [index]  t_current_volume) and (index < last)) do
       inc (index);
   if (index < last) then begin
     t_volumes [index] := t_volumes [last];
   t_volumes [last].Destroy;
   end;
   SetLength (t_volumes, last);
end;

Objects are actually stored via a reference (internal pointer) So t_volumes [last] just points to the objects data

The above statement duplicates the reference

t_volumes [last].Destroy;

destroys the object pointed to by both: t_volumes [last] and t_volumes [index]

You should have destroyed t_volumes [index] *before* copying the value

Martin already said the necessary points, but I'd like to say you a note not related to your problem: if you use "High(t_volumes)" you get the value of the highest index of the array, so you could replace your "last" with that. Just saying...

Regards,
Sven

And you should call Free instead of Destroy.

Jonas

Maybe a bit late, but that might not be true.
If Timothy really talks about _object_ (and not _class(TObject)_) it should work as he does it. Also Destroy would probably be appropriate.

Just saying :-)

The actual type defs used are missing.

Andreas Schneider wrote

Maybe a bit late, but that might not be true. If Timothy really talks about _object_ (and not _class(TObject)_) it should work as he does it. Also Destroy would probably be appropriate. Just saying :-) The actual type defs used are missing.

Unlikely. Quote of Timothy:

How exactly are instantiated classes treated in an array?

So it's very likely that he is indeed talking about descendants of TObject.

Regards,
Sven

Agreed.

BTW, note that reference to "TObject" is not the best solution for differentiation between "old" objects and classes, because TObject type exists for both.

Tomas