Re: Your wish list for Ada 202X

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

On Thu, 24 Apr 2014 20:19:22 -0600, Shark8 wrote:

> On 24-Apr-14 19:22, Randy Brukardt wrote:
>>
>> If one supplies user-defined 'Image, we'd pretty much have to support
>> user-defined 'Value as well. (You wouldn't have to use it, of course). It's
>> rare that only one way I/O is needed. Of course, this ups the effort for
>> composition a lot. I don't think I could support user-defined 'Image without
>> user-defined 'Value -- it seems asymetric to me.
> 
> At that point it sounds like we're getting into the Stream attributes -- 
> though it would be nice to have a secondary IO channel. The distinction 
> is, of course, that user-defined 'Image/'Value would be more geared 
> towards text rather than the generality of streams.

Interestingly that it is already here (A.12.2):

   package Ada.Text_IO.Text_Streams   

Though, there is a big BUT. Since stream attributes rather emulate multiple
dispatch [*] than do full MD, we cannot have your second channel which
would make

   Integer'Output (S, X);

formatting X differently when S is a text file (or a string stream) from
when S is a socket.

-----------
* Stream attributes semantically do cascaded dispatch, first on the I/O
item type, then on the stream type. This precludes stream-dependent
formatting.

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