addprop Adds Properties To Multiple Instances?

I have a class defintion similar to the following:

classdef A < hgsetget & dynamicprops
    %...
end

Then I have another class defintion similar to the following

classdef B < hgsetget
    properties
        a = A();
        b = A();
    end
end

Now here is where it gets weird I, I wrote the following code:

r = B();
e = B();
addprop( get( r, 'a' ), 'p' );
%These two have p.%
disp( properties( get( r, 'a' ) ) );
disp( properties( get( e, 'a' ) ) );
%But these two do not.%
disp( properties( get( r, 'b' ) ) );
disp( properties( get( e, 'b' ) ) );

I double checked the documentation, it states that 'addprop()' adds a property to a class instance. I have taken a few steps after this but none have really worked to well. Could someone explain this behavior to me, or how to work around it, or fix it?

P.s I am using MATLAB R2011b. P.s.s I am a tad new to MATLAB, please excuse any "nooby - ness".

Answer 1

[Chris]

Okay this was a weird one. Apparently when you construct class instances like so:

classdef A
    properties
        b = B();
    end
end

For all instances of that class, 'b' is regarded as the same instance, (static) at least in this context (I have not tested it for other contexts). The solution is to do the following instead:

classdef B < hgsetget
    properties
        a;
        b;
    end
    methods
        function this = B()
            this.a = B();
            this.b = B();
        end
    end
end

This way the interpreter doesent make them (effectivly) static. Sorry if this is a "nooby" reilization, I have only just begun to work with MATLAB.

Answer 2

[Jim Hokanson]

It seems like you have two different issues going on, first, from your question:

classdef B < hgsetget
    properties
        a = A();
        b = A();
    end
end

'a' and 'b' point to different objects, so modifying the properties in 'a' will not change 'b', since they are different instances, and addprop modifies instances, not class definitions. So I would expect that 'b' doesn't have a 'p' property.

From your answer you bring up another issue which was non-obvious to me as well at one point. Matlab evaluates the default properties of each class once unless it is redefined. This means that in your example code (from the original question) 'a' and 'b' will only ever point to two objects, and creating a new B() will not give you new instances.

See the following post under 'defaults': http://blogs.mathworks.com/loren/2011/03/08/common-design-considerations-for-object-properties/#10

Final note, I'm surprised your answer doesn't throw a recursion overflow error, perhaps you meant to assign A() to the properties in the constructor?