Forward declaration of a generic class

[trexet]

Hi. I'm trying to implement a generic class that would hold a circular reference. As I've found, it should be possible starting from FPC 3.0.

The code:

Code: Pascal  [Select][+][-]

1. type
2.  
3.     { TLC_EL_Connector }
4.     generic TLC_EL_Connector<T, TLinked: TEntity> = class;
5.     generic TLC_EL_Connector<T, TLinked: TEntity> = class(TObject)
6.     published
7.         LCFrame: TListControlFrame;
8.     private
9.         type PTEntityList = ^specialize TEntityList<T>;
10.         type LinkedConnector = specialize TLC_EL_Connector<TLinked, T>;
11.     ...
12.     private
13.     ...
14.         Linked: LinkedConnector;
15.     public
16.         procedure Link(constref OtherConnector: LinkedConnector);
17.         procedure AssignData(EList: PTEntityList);
18.         constructor Create(TheOwner: TWinControl);
19.         destructor Destroy(); override;
20.     end;
21.  
22. implementation
23.  

At the implementation line, the complier stops with an Internal Error 200602034. According to FPC source:

Code: Pascal  [Select][+][-]

1.     function FindUnitSymtable(st:TSymtable):TSymtable;
2.       begin
3.         result:=nil;
4.         repeat
5.           if not assigned(st) then
6.            internalerror(200602034);

The error occurs regardless of {$mode ObjFPC} or {$mode delphi}.

FPC 3.2.2, Lazarus 3.4

[Thaddy]

That needs Freepascal trunk.
https://wiki.freepascal.org/FPC_New_Features_Trunk#Support_for_forward_declarations_of_generic_types
FPC 3.2.2 does not have that feature.
Forward declarations are in 3.0 but forward declarations of generic types are only in trunk.

[trexet]

Thanks, managed to overcome this with pointer casting:

Code: Pascal  [Select][+][-]

1. generic TLC_EL_Connector<T, TLinked: TEntity> = class(TObject)
2. private
3.     type PLinkedConnectorObj = ^TObject;
4. private
5.     PLinked: PLinkedConnectorObj;
6.  
7. ...
8.  
9. var Linked: specialize TLC_EL_Connector<TLinked, T>;
10. begin
11.     if PLinked = nil then exit;
12.     Linked := PLinked^ as specialize TLC_EL_Connector<TLinked, T>;