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Newsgroups: comp.lang.ada
Date: Sun, 17 Feb 2019 16:36:23 -0800 (PST)
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Subject: Re: Private extension of a synchronized interface
From: Jere <jhb.chat@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:55555
Date: 2019-02-17T16:36:23-08:00
List-Id: <comp.lang.ada>

On Sunday, February 17, 2019 at 5:36:41 PM UTC-5, Simon Wright wrote:
> Jere writes:
> 
> >   -- The following line gives the error:
> >   -- call to abstract procedure must be dispatching
> >   
> >   --v.p1;
> 
> If you replace this with the dispatching call
> 
>    Example.An_Interface'Class (v).p1;
> 
> it compiles & works just fine.

Good Point!  Thanks!

> 
> I'm far from being an expert on this, because I've never found the need
> to use 'interface' at all, but when you say
> 
>       type An_Interface is synchronized interface;
>       procedure p1(Self : in out An_Interface) is abstract;
> 
>       type Instance is synchronized new An_Interface with private;
> 
> you know that Instance provides a procedure p1, but you don't know
> whether it's a task or protected entry or a protected procedure (or
> even, to my surprise, a plain procedure with that profile, see Ada 2005
> Rationale).
> 
> Of course the compiler knows, so you'd have thought that your v.p1 call
> would be OK (and it _is_ OK if the full declaration of Example.Instance
> is public).
> 
> But the actual problem comes from ARM 3.9.3(7)[1],
> 
>    A call on an abstract subprogram shall be a dispatching call;
>    nondispatching calls to an abstract subprogram are not allowed.
> 
> ... which has been the case since Ada 95!
> 
> [1] http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-3-9-3.html#p7

In the other part that I commented out I was trying to add a publically
available override to the interface operation, but haven't been successful.
Do you know of any syntax changes I might need to do to:

        -- The following lines give the errors:
        -- "p1" conflicts with declaration at line xxx
        -- and
        -- missing body for "p1"
       
        --overriding
        --procedure p1(Self : in out Instance); 

So I don't need to always dispatch?