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Paul
Posts:
18
Registered:
5/18/11


Re: Determining 'classname' such that isa(v,'classname') will be true
Posted:
Apr 17, 2013 9:45 PM


"Steven_Lord" <slord@mathworks.com> wrote in message <kkmaj0$t60$1@newscl01ah.mathworks.com>... > > > "Paul " <paulremovethispartjackson@jhuapl.edu> wrote in message > news:kkki9r$s7c$1@newscl01ah.mathworks.com... > > Given an object v of a class, how can I determine all possible classname > > such that isa(v,'classname') will return true? For example, consider the > > following: > > > > h=ss(1,1,1,1); > > class(h) > > mc=metaclass(h); > > mc.SuperclassList.Name > > L1=isa(h,'ss'); % returns true, understandable > > L2=isa(h,'numlti'); % returns true, understandable > > L3=isa(h,'StateSpaceModel'); % returns true, understandable > > L4=isa(h,'lti'); % returns true, how would I have known? > > [L1 L2 L3 L4] > > > > ans = > > ss > > This comes from class(h) > > > ans = > > numlti > > > > ans = > > StateSpaceModel > > These two come from the _commaseparated list_ mc.SuperclassList.Name. > > > ans = > > > > 1 1 1 1 > > > > I just stumbled on 'lti' returning true for this case. How could I have > > found that programatically? > > Note that while mc is a scalar meta.class object, mc.SuperclassList is a > vector of meta.class objects. ss directly inherits from numlti and > StateSpaceModel. But if you look at the SuperclassList for each of the > elements of the mc.SuperclassList vector of objects, you'll see that numlti > inherits from lti while StateSpaceModel also inherits from another class. > You can walk your way up the inheritance tree using the meta class objects > and their SuperclassList properties until all the meta class objects you > reach have empty SuperclassList properties. > > > In general, is there some function that has a functionality like: > > c = whatis(v); % returns cell array c such that isa(v,c{i}) is true > > Not directly, but you could write one to walk the whole tree. It wouldn't be > that difficult. > > Are you planning to do something tricky and/or clever with this information? > Or is it more something that made you curious? > >  > Steve Lord > slord@mathworks.com > To contact Technical Support use the Contact Us link on > http://www.mathworks.com
Steve,
I missed in the doc that SuperclassList contains only the classes from which the object inherits *directly*. For some reason I thought it would return all of the parents.
I don't think I was trying to do something tricky or clever. I have a function that can take either an ss or tf or zpk object as input and wanted to do a simple error check, like "if ~isa(in,'numlti')", but couldn't find a clear description in the doc for the common class from which those three inherit (there is a diagram in the Control System Toolbox documentation, but it's not what I would think of as an inhertiance tree and doesn't even contain the term 'numlti'). So I started exploring the use of class(h) and metaclass to figure it out myself.
Maybe a whatis type of function would be useful in general to provide insight into a class hierarchy? I don't really use OOP in Matlab, and so don't know if there are any good usecases, other than the one I described above.
Thanks, Paul



