How do I write 'setter' methods for properties with unknown names?

The following class cannot be initialized, as any call to the constructor gives the error:

>> MyClass('a',2)

Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N) to change the limit. Be aware that exceeding your available

stack space can crash MATLAB and/or your computer.

Error in MyClass/MyClass/@(o,p)setProp(o,propname,p)

 

classdef MyClass < dynamicprops
    methods
        function obj = MyClass(propname, val)
            P = obj.addprop(propname);
            P.SetMethod = @(o,p)setProp(o,propname,p);
            obj.(propname) = val;
        end
        function setProp(obj, propname, val)
            % do other stuff, like evaluating if val is legitimate
            obj.(propname) = val;
        end
    end
end

Why is this, and what is the best way to write custom 'set' methods for dynamic properties with unknown names?

Answer 1

[MathWorks Support Team]

The infinite recursion is caused by the line 'obj.(propname) = val;' in setProp. This calls the SetMethod for the property 'propname'. When setting the value of a property, MATLAB checks to see if you are currently in the SetMethod for that property in order to avoid infinite recursion. However, since your SetMethod is an anonymous function which calls setProp (and not setProp itself), this assignment is not inside the SetMethod, and the assignment calls the anonymous function.

To avoid this issue, you may use a nested function as shown below:

% start of file MyClass2.m
classdef MyClass2 < dynamicprops
    methods
        function obj = MyClass2(propname, val)
            P = obj.addprop(propname);
            P.SetMethod = propSetFcn(obj, propname);
            obj.(propname) = val;
        end
    end
end
function f = propSetFcn(obj, propname)
    function setProp(obj, val)
        % do other stuff
        obj.(propname) = val;
    end
f = @setProp;
end
% end of file MyClass2.m