Question

I’m trying to implement a class with a property that can be possibly provided to the constructor or possibly generated in some other method. I don’t want the data saved to disk or generated on load. What I have so far is:

classdef MyClass
        properties(GetAccess = public, SetAccess = private)
            Property1
            Property2
            Property3
        end
        properties(Access = private)
            Property4
        end
        properties(Transient = true)
            ProblemProperty
        end
        properties(Dependent = true, Transient = true)
            Property5
        end

        methods
            function MyClass
                % Constructor.
            end

            function val = get.Property5(B)
                val = SomeFunction(Property1);
            end

            function val = get.ProblemProperty(B)
                if isempty(B.ProblemProperty)
                    B = GenerateProblemProperty(B);
                end
                val = B.ProblemProperty;
            end

            function B = GenerateProblemProperty(B)
                B.ProblemProperty = AnotherFunction(B.Property2);
            end
        end
    end

The problem is that when I try to save the object to disk, Matlab calls the get.ProblemProperty method (confirmed by running the profiler on just the save statement). The ProblemProperty field is empty and I want it to stay that way. It doesn’t call the get.Property5 method.

How do I avoid the call to get.ProblemProperty?

Answer 1

Since the property can sometimes be set (i.e. in the constructor) then this property is not strictly dependent. One solution is to store the settable value in a private property (CustomProblemProperty in the example below) in the constructor. The get method of ProblemProperty would then check return this private property value if it’s not empty and otherwise return the generated value.

classdef MyClass
    properties(GetAccess = public, SetAccess = private)
        Property1
        Property2
        Property3
    end
    properties(Access = private)
        Property4
        CustomProblemProperty
    end
    properties(Dependent = true, Transient = true)
        ProblemProperty
        Property5
    end

    methods
        function B = MyClass(varargin)
            if nargin == 1
               B.CustomProblemProperty = varargin{1};
            end
        end

        function val = get.Property5(B)
            val = SomeFunction(Property1);
        end

        function val = get.ProblemProperty(B)
            if isempty(B.CustomProblemProperty)
               val = AnotherFunction(B.Property2);
            else
               val = B.CustomProblemProperty;
            end
        end

    end
end