OOP: Array object

Hello everyone,

My question is :

i need an array of objects. That array should be able to perform methods like add, remove etc. .

i was thinking about writing a class which has the array as property. Something like this

 classdef MyArray

    properties
        array
    end

    methods
        .
        .
        .
    end

 end

But i noticed that its kind of annoying to always type obj.array to get access to the property.

So, is there any other way to implement an array? Something where an instance of the class itself is an array. Similiar to java.

Thanks in advance!

Answer 1

[Guillaume]

In matlab everything is an array, even classes you design yourself. If you come from other languages such as Java or C++ this is something that can be bit disconcerting. There is no difference between a scalar object and an array object. See for example:

classdef DemoClass
   properties
      value;
   end
   methods
      function this = DemoClass()  %constructor
         this.value = randi(100);
      end
      function sz = howbigamI(this)  
         %the this object to any method can be an array
         sz = size(this);
      end
      function showvalues(this)
         for i = 1:numel(this)
            fprintf('object(%d) has value:%d\n', i, this(i).value);
         end
         fprintf('\n');
      end
   end
end
>> o = DemoClass
o = 
  DemoClass with properties:
      value: 27

>> o.howbigamI
ans =
     1     1

>> o(5) = DemoClass
o = 
  1×5 DemoClass array with properties:  
    value

>> o.howbigamI
ans =
     1     5

>> o.showvalues
object(1) has value:27
object(2) has value:21
object(3) has value:21
object(4) has value:21
object(5) has value:82

You actually have to go out of your way to prevent classes from being used as non-scalar.

[Deasy]

thank you for ur answer. but i am still struggling with my issue. Let me explain it another way.

i have this class for example.

 classdef Graph

    properties
        verticies
        edges
    end

    methods
        .
        .
        .
        % it should look like this
        function addEdge(obj, edge2)
            obj.edges.add(edge2)
        end

    end

 end

verticies and edges will both be (n x 1) arrays of objects. But i also want both of the arrays to have my own custom methods. Like add something to it if its not already in there.

how can i make sure that these arrays have the methods i want them to have? Without making a class as in the original post? This would make edges a object which has the array as property. If i do that it feels like putting an array into another array.

i am not sure if you understand what i mean... But i hope you can help me out. :)

[Guillaume]

You're still making the mistake of thinking in Java. In matlab, an array of edges and an edge are one and the same. A method of the array is a method of the edge.

So, if you want to have custom method for the edge array, you have to add the method to the edge class. That method will apply equally to scalar edge object and array of edge objects.

Answer 2

[Steven Lord]

Some of the topics in this section of the documentation may be interesting and/or of use to you.