Re: generic imports? void* -> generics?

[Simon Wright <simon@pushface.org>]

"Nick Roberts" <nickroberts@blueyonder.co.uk> writes:

> The general idea is that Ada code is able to read a variable from
> the memory area returned by this C function, interpreted as a stream
> array so that the variable's stream-oriented Read procedure or Input
> function can be used directly.

I don't understand this, your suggestion was for Stream_Element_Array
not Root_Stream_Type'Class which is needed for 'Read ..? I can see
that you could wrap a Stream_Element_Array in a Stream, in fact quite
a neat idea! This sort of thing? (would make an interesting addition
to the BCs .. or is this stuff that everybody has known for years &
I've just missed?)

with Ada.Streams;

package Stream_Wrappers is

   type Stream_Wrapper (For_Array : access Ada.Streams.Stream_Element_Array)
   is new Ada.Streams.Root_Stream_Type with private;

   function Last (Used_In : Stream_Wrapper)
     return Ada.Streams.Stream_Element_Offset;

private

   type Stream_Wrapper (For_Array : access Ada.Streams.Stream_Element_Array)
   is new Ada.Streams.Root_Stream_Type with record
      Next_Read : Ada.Streams.Stream_Element_Offset := For_Array'First;
      Next_Write : Ada.Streams.Stream_Element_Offset := For_Array'First;
   end record;

   procedure Read
     (Stream : in out Stream_Wrapper;
      Item   : out Ada.Streams.Stream_Element_Array;
      Last   : out Ada.Streams.Stream_Element_Offset);

   procedure Write
     (Stream : in out Stream_Wrapper;
      Item   : in Ada.Streams.Stream_Element_Array);

end Stream_Wrappers;