[fpc-pascal] question with interfaces, hooks

[David Emerson]

Hi list!

I'm just starting in with interfaces, and am happy to see there is 
something similar to multiple inheritence available. But it seems to be 
limited in a way I will show below, so I am wondering if there is 
something I am missing. Example code says it best...

program test_interfaces;

{$mode objfpc}{$H+}

uses classes, sysutils;

type

   i_foo = interface
     procedure foo;
   end;

   t_foo_base = class (TInterfacedObject, i_foo)
     procedure foo;
   end;

   t_fancy_class_base = class
     // the idea is that I can't reasonably rebase this on t_foo_base
     procedure bar;
   end;

   t_fancy_class = class (t_fancy_class_base, i_foo)
     private
       f_hook : i_foo;
     public
       constructor create; // instantiates f_hook as a t_foo_base
       destructor destroy; override; // destroys the above
       property hook : i_foo read f_hook implements i_foo;
   end;

procedure t_foo_base.foo;
   begin
     writeln ('foo');
   end;

procedure t_fancy_class_base.bar;
   begin
     writeln ('bar');
   end;

constructor t_fancy_class.create;
   begin
     inherited;
     f_hook := t_foo_base.create;
   end;

destructor t_fancy_class.destroy;
   begin
     t_foo_base(f_hook).free;
     inherited;
   end;

var
   fc : t_fancy_class;
   foo : i_foo;

begin
   fc  := t_fancy_class.create;
   foo := t_fancy_class.create;

   fc.foo;          // this won't compile-- why?
   i_foo(fc).foo;   // this works, but is cumbersome

   foo.bar;                // this understandably won't compile
   t_fancy_class(foo).bar; // we can do this if needed
end.


So... since t_fancy_class implements the interface i_foo, why is 
t_fancy_class.foo not available? foo is also generally unavailable from 
within methods of t_fancy_class, an equal frustration.

Is there some mode switch or some such I can use to make it generally 
available?

Thanks!

~David