Hi All,

I have this generic class:

type
  generic TTree<T> = class
  private
    FItems: TList;
    ... ...
  public
    Data: T;
    ... ...
    function FirstChild: TTree;
    ... ...
  end;
function TTree.FirstChild: TTree;
begin
  if FItems.Count = 0 then Exit(nil);
  Exit(TTree(FItems[0]));
end;

when using it, I did:

type
  TStringTree = specialize TTree<string>;

It generated a compilation error:

Error: Incompatible types: got "TTree" expected "TTree$AnsiString"

on the line "Exit(TTree(FItems[0]));" of function FirstChild.

And I tried to change it to:

Exit(TTree<T>(FItems[0]));

But is not accepted.

How to solve this? thanks.

Exit(TStringTree(FItems[0]);

Anyway, isn't better if the children itself is generic? See my gtree implementation:
http://svn.freepascal.org/svn/fpc/trunk/packages/fcl-stl/src/gtree.pp

Could be one of the things I fixed in 2.7.1. Otherwise try the following as a workaround:

=== code begin ===

type
  generic TTree<T> = class
   public type
     TSelfType = TTree;
  private
    FItems: TList;
    ... ...
  public
    Data: T;
    ... ...
     function FirstChild: TSelfType;
    ... ...
  end;
function TTree.FirstChild: TSelfType;
begin
  if FItems.Count = 0 then Exit(nil);
  Exit(TSelfType(FItems[0]));
end;

=== code end ===

I've not tested it though. Just an idea that it might work.

Regards,
Sven

"leledumbo" wrote

Exit(TStringTree(FItems[0]);

Ehm... Who says that TStringTree is available for the generic? Also not every TTree would be a TStringTree?!

Regards,
Sven

TSelfType worked like a charm. Thanks!

Oops, sorry *must be because of my sleepiness :p