What is the correct way to update super class properties?

Question

Grzegorz Lippe 2022-3-8

0
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https://ww2.mathworks.cn/matlabcentral/answers/1666419-what-is-the-correct-way-to-update-super-class-properties

回答： Prince Kumar 2022-3-31

I have a class which serves as a data class for objects with the same pattern. In my example I will use a class Surface:

% Surface.m
classdef Surface 
    properties
        area
        circumference
    end
    methods
        function obj = Surface(area, circumference)
            obj.area = area ;
            obj.circumference = circumference ;
        end
    end
end

Now there are different methods to construct a so called Surface class and since I cannot define multiple constructors for Surface in Matlab I create subclasses which are all of the type Surface, in my example a class Circle.

% Circle.m
classdef Circle < Surface
    properties
        r
    end
    methods
        function obj = Circle(r)
            obj@Surface(0, 0)
            obj.r = r ;
            obj.area = pi * r^2 ;
            obj.circumference = 2 * pi * r ;
        end
    end
end

Now I want a object of type circle to update its superclass properties when its properties are changed. How can I solve this? If the property would be in the class itself I would use a dependent property, but what is the correct pattern, if the property is in a superclass?

% test_classes.m
function tests = test_classes
    tests = functiontests(localfunctions);
end
function test_surface(~)
    area = 2 ;
    circumference = 3 ;
    s = Surface(area, circumference) ;
    assert(s.area == area) ;
    assert(s.circumference == circumference) ;
end
function test_circle(~)
    r = 2 ;
    area = pi * r^2 ;
    circumference = 2 * pi * r ;
    c = Circle(r) ;
    assert(c.area == area) ;
    assert(c.circumference == circumference) ;
end
function test_cicle_change_property(~)
    % Change circle property THIS WILL FAIL
    c = Circle(2) ;   % Create Class
    c.r = 6 ;         % changed property
    r = 6 ;                       % update test values.
    area = pi * r^2 ;             % update test values.
    circumference = 2 * pi * r ;  % update test values.
    assert(c.area == area) ;      % <--   how do I fix this?
    assert(c.circumference == circumference) ;   
end