Reset method being called twice during instantiation of a class instance with inheritance

I'm defining various classes with an inheritance hierarchy and having problems setting up each class's reset method so that it is only called once during instantiation. Here is a toy-example which illustrates the problem.

MySuperClass.m

classdef MySuperClass < matlab.mixin.Copyable
    properties
        a0
        a
    end
    methods
        function obj = MySuperClass(a0)
            obj.a0 = a0;
            obj.reset()
        end
        function reset(obj)
            disp("  MySuperClass reset()")  % for debugging
            obj.a = obj.a0;
        end
    end
end

MyClass.m

classdef MyClass < MySuperClass
    properties
        b0
        b
    end
    methods
        function obj = MyClass(a0, b0)
            obj = obj@MySuperClass(a0);
            obj.b0 = b0;
            obj.reset()
        end
        function reset(obj)
            reset@MySuperClass(obj);
            disp("  MyClass reset()")  % for debugging
            obj.b = obj.b0;
        end
    end
end

The reason I want to call the reset method during instantiation is that the reset operations are quite extensive in the actual implementation and therefore I don't want to duplicate the code in two places or have it run twice.

Test script:

% Test class instantiation
disp("1. Instantiate MySuperClass")
x1 = MySuperClass(0.1); assert(x1.a == 0.1);
x1.a = x1.a + 1;
disp("2. Reset MySuperClass")
x1.reset(); assert(x1.a == 0.1);
disp("3. Instantiate MyClass")
x2 = MyClass(0.1, 0.2); assert(isequal([x2.a x2.b], [0.1 0.2]));
x2.a = x2.a + 1;
x2.b = x2.b + 1;
disp("4. Reset MyClass")
x2.reset(); assert(isequal([x2.a x2.b], [0.1 0.2]));

This executes without errors but it is evident that the reset methods are called twice when instantiating MyClass as shown in the output after '3. Instantiate MyClass' below:

Test script output:

1. Instantiate MySuperClass

MySuperClass reset()

2. Reset MySuperClass

MySuperClass reset()

3. Instantiate MyClass

MySuperClass reset()

MyClass reset()

MySuperClass reset()

MyClass reset()

4. Reset MyClass

MySuperClass reset()

MyClass reset()

I think this is happening because the two lines obj = obj@MySuperClass(a0) and obj.reset() in MyClass.m are both calling reset@MyClass rather than the local methods.

What is the correct way to define these two classes so the reset methods are only called once when an object is instantiated?

Answer 1

[Ishan Gupta]

Calling obj.reset() in the constructor of MyClass is redundant.

This is because while calling obj@MySuperClass(a0); you also call obj.reset() in the superclass constructor here the reset method is already overridden hence reset of MyClass.

In summary obj@MySuperClass(a0); and obj.reset() in MyClass constructor are calling the same reset function of MyClass.

Solution : eliminate obj.reset()

[Bill Tubbs]

Okay, but if I remove the line obj.reset() from MyClass the assertion on line 11 of the test script fails because x2.b has not been initialised to b0. When I instantiate a MyClass object I want it to execute the all reset operations of the parent and the child class.

[Bill Tubbs]

I think this would work if I could put the statement obj.b0 = b0 in MyClass before the call to obj@MySuperClass(a0). Then I could remove the redundant obj.reset(). But in MATLAB you can't assign to obj before the obj = obj@MySuperClass(a0) statement.