Re: Actual stream of a certain type

[Marius Amado-Alves <marius@amado-alves.info>]

Ok, here it goes. Of all idioms I tried maybe the least unsuccessful  
(?) ones are those that raise Program_Error with message  
"accessibility check failed" (GNAT) for line marked HERE below. The  
problem here is: how to use the stream visible on that line, as the  
good T_Stream object he is, pass it as a variable, etc? Thanks a  
great lot.

    type T_Stream_Class_Access is access all T_Stream'Class;

    procedure Write_T
      (Stream : T_Stream_Class_Access;
       Item : in T) is
    begin
       Foobar (Stream.all, Item);
    end;

    procedure Write
      (Stream : not null access Ada.Streams.Root_Stream_Type'Class;
       Item : in T) is
    begin
       if Stream.all not in T_Stream'Class then
          raise Actual_Stream_Must_Be_A_T_Stream;
       else
          Write_T (T_Stream_Class_Access (Stream), Item); -- <== HERE
       end if;
    end;