Is it possible to write "generic" code for TObjectList<T> descendants?

[RaelB 4]

Hi,

 

I create object list collections as below:

 

  TNotes = class(TObjectList<TNote>)
  public
    ...
  end;
  
  TBooks = class(TObjectList<TBook>)
  public
    ...
  end; 
  
  etc..

Is there a way I can write some generic code that will be able to take in TNotes or TBooks instances, for e.g.:

function ListToJSONString(List: TObjectList<T>): string;
begin
...
end;

I want to call as:

  s := ListToJSONString(FNotes) or

  s := ListToJSONString(FBooks)

 

But the function does not compile...

 

Can such a function be declared, or do I need to change my definition of TNotes and TBooks?

 

(I don't like using TObjectList<TNote> or TObjectList<TBook> in my code, since I want to create local (i.e. public) methods for each list type, and it is also simpler writing TNotes instead of TObjectList<TNote> each time)

 

Thanks

Edited December 27, 2021 by RaelB
add a point

[Fr0sT.Brutal 900]

Derive Notes and Books from common generic class that is child of TObjectList with all the common methods you want

Edited December 27, 2021 by Fr0sT.Brutal

[Clément 148]

Have you tried:

 

  TBook = Class

  End;

  TNote = Class

  End;

  TBooks = TObjectList<TBook>;
  TNotes = TObjectList<TNote>;


  TSerializeJSON<T : class> = Class
  private
  public
    function ToJSON<T : Class>( aList : TObjectList<T> ) : String;
  End;

And call it :

 

procedure TForm56.FormCreate(Sender: TObject);
var
  lNotes : TNotes;
  S : TSerializeJSON<TNote>;
begin
  S := TSerializeJSON<TNote>.Create;

  Memo.Lines.text := S.ToJSON<TNote>(lNotes);
end;

This is just to give you an idea. I just compiled and posted

Edited December 27, 2021 by Clément

[RaelB 4]

Thanks, both solutions work for me.

 

with the TSerializeJSON, I can make it a bit simpler (since I am really after a function)

 

  TSerializeJSON = class
  public
    class function ToJSON<T: class>(AList: TObjectList<T>) : string;
  end;

Then i can call without declaring a variable 🙂