在不使用Matlab hgsetget抽象类的情况下定义set / get接口

Question

I generally find the set/get interface defined in hgsetget very useful for setting and getting multiple parameters at the same time. I recently found it was especially suited for object construction. Example:

classdef testclass < hgsetget

    properties
        A
        B
        C
        D
    end

    methods
        function obj = testclass(varargin)
            if ~isempty(varargin)
               set(obj,varargin{:})
            end
        end
    end
end

Usage:

>> a = testclass('A',1,'B',2)

a = 

  testclass handle

  Properties:
    A: 1
    B: 2
    C: []
    D: []

Despite the slowness of this interface I'm really happy of the flexibility it provides.

What is more annoying for my application is that I obtain a handle class (by inheritance from hgsetget).

To circumvent this my first guess was to construct an abstract class with my set/get definition inside. Very simply written it gives:

classdef (Abstract) myAbstractClass

    methods

        function obj = set(obj,varargin)
            for i = 1:2:length(varargin)
                obj.(varargin{i}) = varargin{i+1};
            end
        end

        function val = get(obj,varargin)
            val = cell(length(varargin),1);
            for i = 1:length(varargin)
                val{i} = obj.(varargin{i});
            end
        end

    end  

end

and then set it as superclass for my test class

classdef testclass < myAbstractClass

    properties
        A
        B
        C
        D
    end

    methods
        function obj = testclass(varargin)
            if ~isempty(varargin)
                set(obj,varargin{:})
            end
        end
    end
end

However I must misunderstand something in the construction mechanism because here is what happens:

>> a = testclass('A',1,'B',2)

ans = 

  testclass

  Properties:
    A: 1
    B: 2
    C: []
    D: []

  Methods, Superclasses


a = 

  testclass

  Properties:
    A: []
    B: []
    C: []
    D: []

  Methods, Superclasses

If somebody knows the reason of this behavior, I'm totally open to her/his explanations

Thank you in advance

JM

Answer 1

Overall your design looks good, but within your constructor method testclass , you need to write

obj = set(obj,varargin{:});

Because you are using a value class rather than a handle class, you need to retrieve the output of your set method, otherwise you'll have set the property of something, and then discarded it and returned a completely different (and empty) obj as output.

Also, you need to add a semi-colon after the call to set ; otherwise it will display the intermediate something.

You may also want to revise your opinion of handle classes; they're really very natural to use (just my opinion, but more natural in an OO context than value-behaviour).