Re: Reprise: 'in out' parameters for functions

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

Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:c5b6pt$2pcs4d$2@ID-77047.news.uni-berlin.de...
> ...
>> Provided that:
>>
>> 1) protected object and tasks would be tagged (inheritable from);
>> 2) multiple inheritance would be supported;
>> 3) entries, procedures and functions would be primitive operations;
>> 4) functional notation would be permitted (instead of prefix notation)
> 
> See AI-345, which extends the interface mechanism (itself a Ada 200y
> proposal) to cover task and protected types. (1) is true if the PT or TT
> inherits from one or more interfaces; (2) follows from the definition of
> interfaces; (3) is true for calls through interfaces (as opposed to
> directly to the PO or TOs); (4) is true for calls through interfaces.
> 
>> one could have entries of multiple protected objects and tasks.
> 
> I don't see how this follows from (1) to (4), though. Each call is just a
> dispatching call to a single operation; there is no implementation
> inheritance.

Yes, but if I could have two dispatching parameters of same protected type
(no MD involved) in a primitive operation, then a call to it should start
two protected actions. Same with task entries, (4) should allow something
like:

task type Foo is ... end Foo;
entry Double_Rendezvous (X, Y : in out Foo);
   -- Declared after "end Foo";

task body Foo is
begin
   loop
      accept Double_Rendezvouz;
         -- Cannot give the body here
   end loop;
end Foo;

entry Double_Rendezvouz (X, Y : in out Foo) is
begin
   ...
end Double_Rendezvouz;

[ I cannot see any direct use of things like that, except for demonstrating
race conditions to students (:-)), but who knows... ]

>> A call to such entry would start multiple protected actions (one per each
> protected
>> object parameter) and multiple rendezvous (one per each task object
>> parameter). Could we agree that 1-4 is a damn *lot* of work?
> 
> Not really. *Interfaces* is a lot of work, but presuming that we're going
> to have those anyway, adding protected and task support to them is not a
> significant increment.

I am glad to hear it from you, because of course, you know it better.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de