RE: Re: Class Inheritance

[Kevin Hawkins]

Can I try and move this forward so that we have an agreement on class
inheritance here and a way of managing it. I note the xPL guys are now
talking about the same issue having found that a having only one level of
inheritance from a .basic class is not proving adequate. The way we have
implemented class.type as an n level inheritance and also the message body
names with n levels is a huge advantage here.

Kevin

> -----Original Message-----
> From: Kevin Hawkins [mailto:<a
href="/group/xAP_developer/post?postID=ef1aspmN8OfjgYJE7KKDHO3lPc2Te_PQ56xVEZ6Vd8wsJz0yeVS0zatkCPCTahU4qvEGNvVaEHdj5pWvr3EH">lists@u...</a>]
> Sent: 27 May 2003 23:54
> To: <a
href="/group/xAP_developer/post?postID=Zr2PrpKGu-jMT-5kQ2TAJkhKrFZ4o6wCWnuiGCpW8iL4LfifpkMkWfXn1rSaup7vxLiDHB-i-OFYy1e4OyQZSMTqglwt">xAP_developer@xxxxxxx</a>
> Subject: RE: [xAP_developer] Re: Class Inheritance
>
> Sorry guys,
>
> I have a domestic issue that has cropped up that is taking my
> time -
> back very shortly - keep up the discussions - and please raise any of
> the
> other topics too - hopefully it will be all sorted in a couple of days
> time.
>
> K
>
> > -----Original Message-----
> > From: Stuart Booth [mailto:<a
href="/group/xAP_developer/post?postID=aPmjZntMa3UZtOy7hGJdT2g9NQ_rYNGT2SiOoGNSMgfVH72TLFI0XVLBMbWLxqPnjZbg85n0Om0mxAwO">lists@s...</a>]
> > Sent: 25 May 2003 11:31
> > To: <a
href="/group/xAP_developer/post?postID=Zr2PrpKGu-jMT-5kQ2TAJkhKrFZ4o6wCWnuiGCpW8iL4LfifpkMkWfXn1rSaup7vxLiDHB-i-OFYy1e4OyQZSMTqglwt">xAP_developer@xxxxxxx</a>
> > Subject: Re: [xAP_developer] Re: Class Inheritance
> >
> > On Sun, 25 May 2003 09:50:58 -0000, "Patrick Lidstone"
> > <<a
href="/group/xAP_developer/post?postID=CDoii3mbosZG0jzsUjcmGj0Qfk7c39EgPLTfP-OkPToXopljAwo1vT8uaxnod72WNf9owdG8FC1aFkEnfW4">patrick@l...</a>>
wrote:
> >
> > >> But here I'm thinking that the derived class schema
alters the
> > >> formatting/meaning of the value entirely.
> > >
> > >Not sure I've understood you PoV here.
> >
> > Ahh, I'm just mentioning the various ways I was interpreting your
> own
> > thoughts. Reinterpreting vs Redefining were the two ways I
thought
> of
> > based on what you'd suggested.
> >
> > > We cannot allow a derived
> > >class to redefine a base class element, only to extend the
class.
> > >Otherwise no device that understands just the base class can
make
> use
> > >of it, because the meaning of a particular value may have
> changed!
> >
> > Great! I didn't much like that either.
> >
> > >There's an argument to be made for calling the block
> > >audio.transport.meridian since the base class can be derived
> > >implicitly, and this adds a clear indication of the expected
> block
> > >content when it is broken apart from the header.
> >
> > So here then, a Class of xAP-Audio.Transport.Meridian demands a
> block
> > name of Audio.Transport.Meridian.
> >
> > But an app listening for xAP-Audio.Transport messages could still
> pick
> > up the xAP-Audio.Transport components and ignore anything it
> doesn't
> > recognise.
> >
> > It could still read the Audio.Transport.Meridian block, but only
> deal
> > with Audio.Transport items/values, ignoring the rest. This
passes:
> >
> > Audio.Transport.Meridian
> > {
> > Command=scan
> > }
> >
> > And if the block was named Audio.Transport, anything not part of
> the
> > Audio.Transport block would instead be flagged as invalid. This
> fails:
> >
> > Audio.Transport
> > {
> > Command=scan
> > }
> >
> > Just a thought on message validation.
> >
> > >I have thought of one problem with the MI arrangement. What
> happens
> > >if you want to control more than one "thing" in one
message (ie
> > >repeat the same class more than once, in a different control
> context
> > >each time - perhaps to set a lighting scene) - you can't
identify
> the
> > >significance of each block because it doesn't have a name.
You
> could
> > >solve this easily enough by changing the format of the block
name
> to
> > >be say <class>:<label> where :<label> is
optional. It's a big
> deal to
> > >change the naming scheme, but it's also a big deal to limit
> messages
> > >to only controlling a single thing...
> > >
> > >Splitting two pieces of control information that belong
together
> into
> > >separate messages is a really bad idea. It means that the
> receiver
> > >has to be stateful (difficult on say a PIC), and it means
that
> you
> > >can have all sorts of unintended behaviour if messages arrive
out
> of
> > >order or if message gets lost.
> >
> > Oh, yes, of course. That makes perfect sense.
> >
> > S
> > --
> > Stuart Booth
> > xAPFramework.net - a reusable xAP framework for .net
> >
> > <a href="http://www.xapframework.net/";>http://www.xapframework.net/</a>
<a
href="/group/xAP_developer/post?postID=0fW_lhAPo1WSG4snxA1WSc9Xn7ThpLJtd8YVWKd22ucLu357ReRnzbeZS3nVsVGaX9Z_L6jUGIT6Fdu8PvjbIMXT">stuart@x...</a>
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