[lazarus] How to do a cast in fpc (i'm just stuck in doors)

[marius popa]

Want to do a cast from "VOID_POINTER" to "TFIBBASE" because 
of this  error :

Compiling fibdatabase.pp
fibdatabase.pp(529,22) Error: Incompatible types: got "VOID_POINTER" expected "TFIBBASE"
fibdatabase.pp(568,26) Error: Incompatible types: got "VOID_POINTER" expected "TFIBTRANSACTION"

and here is my 529 offensing line :

function TFIBDatabase.GetDataSet(Index: Integer): TFIBBase;
begin
  result := FDataSets[Index];
end;

where TFIBase is :
  TFIBBase = class(TObject)
  protected
    FDatabase: TFIBDatabase;
...........................
  end;
and FDataSets is declared :

  FDataSets           : TList;