Accessing a property or method when inheriting from RedefinesDot

Question

Antonio Hortal 2023-8-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2011867-accessing-a-property-or-method-when-inheriting-from-redefinesdot

评论： James Lebak 2023-9-11

When inheriting from matlab.mixin.indexing.RedefinesDot, I have noticed that dot-indexed properties do not trigger the dotReference or dotAssign methods

A simple example:

classdef MyDotClass < matlab.mixin.indexing.RedefinesDot && ...
                      matlab.mixin.indexing.OverridesPublicDotMethodCall 
    properties
        MyProperty = 1
    end
    methods (Access = protected)
        function out = dotReference(this, idxOp)
            out = [];
            disp("Dot referencing [" + idxOp(1).Name + "]")
        end
        function out = dotAssign(this, idxOp)
            out = [];
            disp("Dot assigning [" + idxOp(1).Name + "]")
        end
        function n = dotListLength(this, idxOp, idxContext)
            n = 1;
        end
    end
end

m = MyDotClass();
result = m.MyProperty; % result = 1; (And doesn't print)
result = m.RandomThings; % result = []; (And prints >> Dot Referencing [RandomThings]

Inheriting from matlab.mixin.indexing.OverridesPublicDotMethodCall solves the issue for when public methods are called, but not for properties. Also, this behaviour is different than with subsref and subsassign, which actually trigger when a property is used.

My question is: is there is a way to also capture properties in the dotAssign and dotReference?

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James Lebak 2023-9-11

No. This is by design. RedefinesDot does not override properties that are accessible in the present context.

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Answer 1

Yash 2023-8-30

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在 MATLAB Online 中打开

Hi @Antonio Hortal

You are correct in your observation that when inheriting from matlab.mixin.indexing.RedefinesDot, the dotReference and dotAssign methods are not triggered when accessing properties. This is because these methods are designed to work with indexing operations, not property access.

Property access in MATLAB is typically handled by the get and set methods. When you access a property using dot notation (e.g., obj.Property), MATLAB automatically calls the get method to retrieve the property value. Similarly, when you assign a value to a property (e.g., obj.Property = newValue), MATLAB calls the set method to perform the assignment.

If you want to capture property access and assignment, you should override the get and set methods in your class, like this:

classdef MyDotClass < matlab.mixin.indexing.RedefinesDot && ...
        matlab.mixin.indexing.OverridesPublicDotMethodCall 
    properties
        MyProperty = 1
    end
    methods
        function value = get.MyProperty(this)
            disp("Getting MyProperty");
            value = this.MyProperty;
        end
        
        function this = set.MyProperty(this, value)
            disp("Setting MyProperty");
            this.MyProperty = value;
        end
    end
    
    methods (Access = protected)
        function out = dotReference(this, idxOp)
            out = [];
            disp("Dot referencing [" + idxOp(1).Name + "]")
        end
        
        function out = dotAssign(this, idxOp)
            out = [];
            disp("Dot assigning [" + idxOp(1).Name + "]")
        end
        
        function n = dotListLength(this, idxOp, idxContext)
            n = 1;
        end
    end
end

With these modifications, you can capture property access and assignment in your class. When you access or assign the MyProperty property, the get and set methods will be called, and you can insert your custom logic there.

I hope this helps.

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Antonio Hortal 2023-8-30

Thanks a lot @Yash for the reply!

I'd argue that if there's a way to override method calls it (inheriting from matlab.mixin.indexing.OverridesPublicDotMethodCall), it would also make kind of sense to have a similar way to override property referencing and assignment. But I get this would be another that is already covered with the property getters and setters.

I will stick with subsref and subsasgn for now :)

Thanks again

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