Re: Messing with access types...

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2020-12-28 19:56, Marek wrote:

> I think I'll try another approach: just write extra layer in C, which
> will direct communicate with host and will provide prepared data for Ada
> part.

The standard approach is somewhat different:

1. Thin Ada bindings mapping to C, mostly 1-to-1 with minor adjustments, 
e.g.

- replacing BOOL with Ada Boolean
- translating C strings into Ada Strings
- replacing C pointer parameters with Ada out or in out, as appropriate
- making proper functions where C cannot, e.g. returning string results 
where C API uses a buffer to store string copy. The buffer is made 
local, C function is called to fill it. Then the contents is converted 
to Ada string and returned out.

2. On top of that you do thick Ada bindings:

- reasonable interfaces
- all implementation types made private
- return codes replaced with exceptions
- C's malloc/free pairs wrapped by Ada controlled types
- similarly resources seizing/releasing pairs go into controlled types
- messages/events loops encapsulated into Ada tasks
- these tasks are wrapped by a controlled type (AKA active object)

You do not need to change anything on the C side. You can incrementally 
advance #2 as far as you feel necessary since you can always fall back 
to #1.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de