MATLAB: Update a value class property only if required

Question

Hello everyone,

I am new to object oriented programming and have some issues getting the behavior of my class in the way I want it. I have several input properties and a "dependent" output property. Because the algorithm to compute the output is numerically intensive, I do not want to handle it as an actual dependent property. It should only be updated if necessary. Also I want to be able to save my results to my hard drive, which would not work with a dependent property.

I got this basically working if my class is a handle class as shown in the example down below. But I do not like how handle classes function. In particular it can be very unintuitive to the user if they try something like this:

A = myclass(1,2); 
B = A; 
A.input1 = 5;

So here is my example with the handle class. Can anyone tell me if that can also be achieved with a value class? General improvement suggests are welcome as well 🙂

Thanks a lot in advance!

classdef myclass < handle
    properties
        input1
        input2
        output
        update_required
    end
    
    methods
        
        function obj = myclass(value1, value2)
            
            obj.input1 = value1;
            obj.input2 = value2;
            obj.output = [];
        end
        
        function set.input1(obj, value)
            
            if obj.input1 == value
                return
            end
            
            obj.input1 = value;
            obj.update_required = true;
        end
        
        function set.input2(obj, value)
            
            if obj.input2 == value
                return
            end
            
            obj.input2 = value;
            obj.update_required = true;
        end
        
        function value = get.output(obj)
            
            if obj.update_required
                disp('Update required.')
                obj.output = obj.input1 + obj.input2;
                obj.update_required = false;
            else
                disp('No update required.')
            end
            
            value = obj.output;
            
        end
    end
end

Answer 1

I think my solution works if you reset your update_required within your if...end block.

classdef myclass
    properties
        input1
        input2
    end
    
    properties (Dependent = true)
        output
        update_required
    end
    
    properties (Hidden = true)
        output_
        update_required_
    end
    
    methods
        
        function obj = myclass(value1, value2)
            
            obj.input1 = value1;
            obj.input2 = value2;
            obj.output = value1 + value2;
        end
        
        function obj = set.input1(obj, value)
            
            if obj.input1 == value
                obj.update_required = false;
                return
            end
            
            obj.input1 = value;
            obj.update_required = true;
        end
        
        function obj = set.input2(obj, value)
            
            if obj.input2 == value
                obj.update_required = false;
                return
            end
            
            obj.input2 = value;
            obj.update_required = true;
        end
        
        function value = get.output(obj)
            
            if obj.update_required
                disp('Update required.')
                obj.output = obj.input1 + obj.input2;
                obj.update_required = false;
            else
                disp('No update required.')
            end
            
            value = obj.output_;
            
        end
        
        function obj = set.output(obj, val)
            obj.output_ = val;
        end
        
        function val = get.update_required(obj)
            val = obj.update_required_;
        end
        
        function obj = set.update_required(obj, val)
            obj.update_required_ = val;
        end
    end
end
>> A = myclass(1, 2);
>> A
A = 
Update required.
  myclass with properties:
             input1: 1
             input2: 2
             output: 3
    update_required: 1
>> A.input1 = 1
A = 
No update required.
  myclass with properties:
             input1: 1
             input2: 2
             output: 3
    update_required: 0
>> A.input2 = 2
A = 
No update required.
  myclass with properties:
             input1: 1
             input2: 2
             output: 3
    update_required: 0
>> A.input1 = 5
A = 
Update required.
  myclass with properties:
             input1: 5
             input2: 2
             output: 7
    update_required: 1
>> A.input2 = 10
A = 
Update required.
  myclass with properties:
             input1: 5
             input2: 10
             output: 15
    update_required: 1