[fpc-pascal] Assigning a virtual class method to a method pointer

[Joao Morais]

Hello,

I need to check if a virtual class method was implemented in an specific
subclass. I am assigning two methods to two method pointers, casting to
tmethod and comparing its code fields. The application raises a
segmentation fault in this line:

     vmethodptr2 := @tbaseclassref(classparent).classmethod;

The following code raises the exception using both 2.0.4 and 2.1.1.

====
{$mode objfpc}

program testclass;

type
   tbaseclassref = class of tbaseclass;

   tbaseclass = class(tobject)
   public
     class function classmethod: string; virtual;
     class function implementsclassmethod: boolean;
   end;

   tinheritedyesclass = class(tbaseclass)
   public
     class function classmethod: string; override;
   end;

   tinheritednoclass = class(tbaseclass)
   end;

class function tbaseclass.implementsclassmethod: boolean;
var
   vmethodptr1, vmethodptr2: function: string of object;
begin
   if self <> tbaseclass then
   begin
     vmethodptr1 := @classmethod;

     // here is the problem
     vmethodptr2 := @tbaseclassref(classparent).classmethod;

     result := tmethod(vmethodptr1).code <> tmethod(vmethodptr2).code;
   end else
     result := false;
end;

class function tbaseclass.classmethod: string;
begin
   result := '';
end;

class function tinheritedyesclass.classmethod: string;
begin
   result := 'some stuff';
end;

const
   cboolvalues: array[boolean] of string = ('no', 'yes');

begin
   writeln(cboolvalues[tinheritedyesclass.implementsclassmethod]);
   writeln(cboolvalues[tinheritednoclass.implementsclassmethod]);
end.
====

Am I doing something wrong or this is a bug?

Thanks,
--
Joao Morais