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From: "Alejandro R. Mosteo" <alejandro@mosteo.com>
Newsgroups: comp.lang.ada
Subject: Re: interfaces and limited/controlled/limited-controlled types
Date: Wed, 31 Jan 2018 12:54:46 +0100
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Date: 2018-01-31T12:54:46+01:00
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On 27/01/18 08:12, Randy Brukardt wrote:
> "Alejandro R. Mosteo" <alejandro@mosteo.com> wrote in message
> news:p4f2oa$c4u$1@dont-email.me...
> ...
>> I just was lamenting myself recently for not recalling this idea for the
>> next revision. Just add new interfaces with the same semantics.
> 
> That would probably work for Root_Storage_Pool and Root_Streams as these
> generally don't have any associated implementation.
> 
> For controlled, however, a common implementation strategy is to build the
> overhead into the root type (the chaining components that are common to all
> controlled object). Interfaces can't have components, and the work to allow
> that in this one case is roughly equivalent to allowing all interfaces to
> have components (which of course is full multiple inheritance -- which would
> make Dmitry happy :-). I don't see any point in doing a massive amount of
> work inside the compiler and not letting users have access to it. So it
> essentially is full MI or bust here (and I personally vote for bust :-).

I understand now, thanks. I had considered the user side POV only, 
thinking that some "compiler magic" would be involved, but certainly 
didn't suspect it would be so big a change.

Thanks,
Alex.

> 
>> I wonder if there are technical problems besides having a duplicated
>> feature.
> 
> If there is any concrete implementation associated with the root type, then
> an interface is not a useful replacement. You would need multiple
> inheritance to work for abstract types (in which case interfaces are a junk
> redundant feature). Most likely, existing vendors would just forget about
> upgrading their compilers (that seems to be the case for some vendors
> anyway, wouldn't want to make it a perfect sweep :-).
> 
>                                       Randy.
> 
>