Hello,

It was many years ago i tried fpc/lazarus so i'm not up to speed with eveything. At this moment I'm trying to rewrite a piece of software from delphi to fpc/laz and i'm having trouble rewriting generics and in special the TObjectDictionary. Below shows how it is implemented in delphi.

Is there a native fpc solution for this and if there is not what are the alternatives to rewrite this? Or would it even be better to avoid generics in general?

TMyDic = TObjectDictionary <string, TMyObject>;

I would welcome any tips to solve this

Thanks,
Marius

I'm using fpc 2.7.1, laz 1.1(svn 4/7/13)

Hi,

Ever tried TStringList with Strings[] and Objects[] properties?

kind regards,
Dimitri Smits

----- Oorspronkelijk e-mail -----

Thanks Dimitri,

Yes, I have used it lots of times and its really the last choice if theres something available like the objectdictionary. In this case the dict is also the owner of the objects, it saves me the continious ugly typecasting, takes care of the extra administration with freeing objects and all the additional troubles you get over time with this solution (its not as bad as i'm telling now). In other words tstrings.objects are working fine, but i find it a bad strategy if you have to use it in flatout in the whole application.

I'm curious how to rewrite/solve dictionaries, indexed list and even sorted strings.objects to a neat solution while (if possible) working with both delphi and fpc/laz.

Greetings,
Marius

"Dimitri Smits" wrote

Hi, Ever tried TStringList with Strings[] and Objects[] properties?

The speciality of TObjectDirectory is that it frees the objects when an entry is deleted (similar to TObjectList).
But I now remember that we added an OwnsObjects property to TStringList some time ago...

Regards,
Sven

In our previous episode, Marius2 said:

There is fgl.tfglmap and variants.

But AFAIK we don't have a TFGLObjectMap...

Regards,
Sven

You can always use functions, to fight typecasting.

function GetMyObject(dic: TStrings; const nm: string): TMyObject;
var
  i : integer;
begin
  if not Assigned(dic) then begin Result:=nil; Exit; end;
  i:=dic.indexof(nm); // replace with IndexOfName if necessary
  if (i<0) or (i>=dic.Count) or not (i.Objects[i] is TMyObject) then
Result:=nil
  else Result:=TMyObject(i.Objects[i]); // not using "as" , since "is" has
already been used
end;

Of course, people would use ClassHelpers these days to have nice syntax and avoid the sanity check.

thanks,
Dmitry

please disregard my last note about "avoiding the sanity check"

On Mon, Apr 8, 2013 at 1:52 PM, dmitry boyarintsev <

use the following unit:

unit StringMyObjectMap;
{$mode objfpc}{$H+}
interface
uses ghashmap;
type
  TStringHash = class
    class function hash(s: String; n: Integer): Integer;
  end;
  TMyObject = class ... end; // define yourself
  TStringMyObjectMap = class(specialize
THashMap<String,TMyObject,TStringHash>)
    destructor Destroy; override;
  end;
implementation
class function TStringHash.hash(s: String; n: Integer): Integer;
var
  c: Char;
begin
  Result := 0;
  for c in s do Inc(Result,Ord(LowerCase(c))); // remove LowerCase if you
want the key search to be case sensitive
  Result := Result mod n;
end;
destructor TStringMyObjectMap.Destroy;
var
  It: TIterator;
begin
  if Size > 0 then begin
    It := Iterator;
    repeat
      It.Value.Free;
    until not It.Next;
    It.Free;
  end;
  inherited Destroy;
end;
end.

WARNING: untested code, though I'm quite sure it works fine

Marco van de Voort wrote

There is fgl.tfglmap and variants.

Thank you Marco,

I was aware of this class but have to study it more nefore using it..

dmitry boyarintsev wrote

function GetMyObject(dic: TStrings; const nm: string): TMyObject;

It is one of the few solutions to share the code between delphi and fpc (and yes, i would probably encase it in another class to hide the typecasting). Still need to figure out how hashing compare to stringlist (it should be a lot faster but i can't find the link at this moment)

(Sorry I had some trouble with the mailing list, previous msg's are delayed)

Sven Barth wrote

But I now remember that we added an OwnsObjects property to TStringList some time ago...

Magic, I honestly have to admitt I was not aware of that, thanks!

leledumbo wrote

use the following unit: unit StringMyObjectMap;

Thanks,

That is a pretty advanced piece of generics, I found the fpc sources together with the hasmapexample. I'm afraid i need to play to get comfortable with generics g> but it will get me on my way..

(Sorry I had some trouble with the mailing list, previous msg's are delayed)

Oops, my bad. There's actually a bug in the search. It will still be case sensitive despite the hash function uses lowercase-d version of the key. It only affects the items distribution, but the key is still searched in case sensitive way through the selected bucket.