Overload only several functions

Question

Zoltán Csáti 2014-10-18

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159129-overload-only-several-functions

评论： Zoltán Csáti 2014-10-20

Hi,

I am totally new to Matlab OOP. For my program to work, I need to redefine the built-in min, max and abs functions. However, if I declare these three functions as methods, all the other functions like sine, cosine, etc. must be declared so that they act on the defined object. So how can I only redefine (overload) these three functions and let the others unchanged.

Thanks, Zoli

2 个评论
显示无隐藏无

Image Analyst 2014-10-18

I believe redefining is usually called overriding, not overloading which is somewhat different because with overloading you can have different functions and it figures out which to use based on what inputs you pass and outputs you accept.

Zoltán Csáti 2014-10-20

Thank you for explaining the difference.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Guillaume 2014-10-18

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159129-overload-only-several-functions#answer_155687

It sounds like you're trying to implement a numeric class. So I'll refer you to matlab own's documentation on subclassing built-in classes

If you derive from a numeric class (e.g. double), you'll automatically get all the methods that apply to double, and you can override the one you want.

Otherwise, there's no other way than you writing all of them, even if it's just a dispatch to the built-in ones.

6 个评论
显示 4更早的评论隐藏 4更早的评论

Guillaume 2014-10-19

在 MATLAB Online 中打开

Unfortunately, the documentation is quite explicit about this. Built-in methods that operate on data values return objects of the superclass. With matlab class system, I'm afraid there's no way around it but to override the methods in your class and just dispatch to the base class.

There's not that many so it shouldn't be too much of a hassle. You still get free inheritance of the indexing, reshaping, concatenating, etc. methods, as long as your subclass does not have any properties.

In your example above, you've defined a property but it serves no purpose as it stores the exact same value as the one stored in the double base class. You could rewrite your class as:

classdef complexredefine < double
   methods
      function obj = complexredefine(a)
         if nargin < 1   %you should also add that for user-friendliness
            a = 0;
         end
         obj = obj@double(a); 
      end
        function y = abs(obj)
            if real(obj) < 0
                y = complexredefine(complex(-real(x),-imag(x)));
            else
                y = abs@double(obj);
            end
        end
     end
  end

and it would work just the same with the addition that you can no index into it.

Guillaume 2014-10-20

As I said:

With matlab class system, I'm afraid there's no way around it but to override the methods in your class and just dispatch to the base class.

There's not that many so it shouldn't be too much of a hassle

Zoltán Csáti 2014-10-20

Thank you, I will do it.

请先登录，再进行评论。

Answer 2

Geoff Hayes 2014-10-18

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159129-overload-only-several-functions#answer_155667

在 MATLAB Online 中打开

Zoltán - have you created a new class that you wish to implement the max, min, and abs functions for? Or are you trying to overload these three functions for all data types?

If the former, then why not try something like the following

 % class definition
 classdef MyClass < handle
    % private data members
    properties (Access=public)
        attribute1;
        attribute2;
    end
    methods (Access=public)
        % class constructor
        function [obj] = MyClass(attr1,attr2)
            obj.attribute1 = attr1;
            obj.attribute2 = attr2;
        end 
        % returns the instance of MyClass in the array with the greatest
        % attribute2 property
        function [maxObj] = max(myClassArray)
            maxObj = myClassArray(1); 
            for k=2:length(myClassArray)
               if maxObj.attribute2 < myClassArray(k).attribute2
                   maxObj = myClassArray(k);
               end
            end
        end
        % returns the instance of MyClass in the array with the smallest
        % attribute2 property
        function [maxObj] = min(myClassArray)
            maxObj = myClassArray(1); 
            for k=2:length(myClassArray)
               if maxObj.attribute2 > myClassArray(k).attribute2
                   maxObj = myClassArray(k);
               end
            end
        end        
        function display(obj)
            fprintf('Attribute 1 = %f Attribute 2 = %f\n',...
                    obj.attribute1, obj.attribute2); 
        end
    end
end

The above definition is for a very simple class with two attributes. We define the max and min methods to determine that instance (of this class) in the input array that has the maximum attribute2 property and the minimum attribute2 respectively. For example,

 myObjA = MyClass(1,2);
 myObjB = MyClass(3,4);
 myArray = [myObjA myObjB];
 maxObj = max(myArray);
 minObj = min(myArray);

In the above, we can see that maxObj corresponds to myObjB, and minObj corresponds to myObjA.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Geoff Hayes 2014-10-18

在 MATLAB Online 中打开

Try using the builtin function so we can call the MATLAB builtin function from our overloaded method.

Add the following method to the above class

 % calculate the sine of attribute 1
 function [result] = sin(obj)
     result = builtin('sin',obj.attribute1);
 end

Now, try the following

 clear all;
 myObjA = MyClass(pi/4,12);
 sin(myObjA)

and we get the expected answer of sin(pi/4) as

 ans =
         0.707106781186547

As for your question concerning handle, see the abstract class for deriving handle classes for more details.

Zoltán Csáti 2014-10-18

Thank you too, especially for the link pointing at subclass and builtin.

请先登录，再进行评论。

Overload only several functions

2 个评论
显示无隐藏无

采纳的回答

6 个评论
显示 4更早的评论隐藏 4更早的评论

更多回答（1 个）

3 个评论
显示 1更早的评论隐藏 1更早的评论

另请参阅

类别

标签

产品

Community Treasure Hunt

Overload only several functions

2 个评论 显示 无隐藏 无

采纳的回答

6 个评论 显示 4更早的评论隐藏 4更早的评论

更多回答（1 个）

3 个评论 显示 1更早的评论隐藏 1更早的评论

另请参阅

类别

标签

产品

Community Treasure Hunt

2 个评论
显示无隐藏无

6 个评论
显示 4更早的评论隐藏 4更早的评论

3 个评论
显示 1更早的评论隐藏 1更早的评论