Creating a class object with the same class name as a variable

Suppose I have 10 classes defined well, with class names as a1,a2,a3...a10. A key variable K indicates which class object I should create.

For example, when K='a1',obj=a1();
             when K='a2',obj=a2();
           .....

I don't want to use switch or other similar control commands, since the class library is always expanding, more classes definitions will be added. I aim to find a good way to create corresponding class object with the least change, like obj=K(),where K=a1,a2,a3....but absolutely this doesn't work.

Is there any way to solve this problem? Thanks a lot!

[Stephen]

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[Adam]

How is 'K' created?

Ideally it should contain a function handle to the constructor of the class you want to create an object of rather than a string.

I am assuming that your classes are not really named a1, a2, a3, etc and that is just for the purposes of the question, otherwise you really need to find some meaningful names for your classes!

[Guillaume]

More details about the purpose of these classes would greatly help in giving you the right answer. Depending on this the answer could be: Don't do this your design is flawed, use a class factory function, use inheritance from an abstract base class, something else or a combination of these.

Answer 1

[Sayyed Ahmad]

I creat some file which is called: CLASS_Template.m and used some KEY_CLASSNAME as a key in this template.

      %codes of CLASS_Template:
      classdef test
          properties (SetAccess='public', GetAccess='public')
              prop;
          end 
          properties (SetAccess='private', GetAccess='public')          
          end
          properties(SetAccess='private', GetAccess='private')          
          end      
          methods
              function o=test(varargin)
                  switch nargin
                      case 1
                          o.prop = varargin{1};
                      otherwise
                          error('the number of input proprties doesn''t macht.')
                  end
              end          
              function display(o)
                  disp('<a href="matlab: helpwin test">test properties:</a>')
                  disp(o.prop);
              end     
              function disp(o)
                  display(o)
              end     
              function help(o)
                  helpwin test
              end
          end
      end

in the second file called CreateClass would the Key replaced with the className.

function CreateClass(varargin)
    classname = varargin{1};
    dirname = ['@' classname];
    str_date=datestr(date,'dd.mmm.yyyy');
    [status,message,messageid]=mkdir(dirname);
    pause(1);
    fid = fopen('/Path_to_Template/CLASS_Template.m');
    F = fread(fid, '*char')';
    fclose(fid);
    F=strrep(F, 'KEY_CLASSNAME', classname);
    F=strrep(F, 'KEY_DATE', str_date);
    cd([pwd '\' dirname]);
    fid = fopen([classname '.m'], 'w');
    fwrite(fid, F);
    fclose(fid);
    open([classname '.m'])
end

Now you can run the following command

>>CreateClass test

Depending on your needs you could have more than one key.

I hope you have your answer.

cheers! Ahmad

Answer 2

[per isakson]

You could create a function, factory, to communicate the intent.

K = 'a1';
obj = factory( K );

where

function    obj = factory( name )
    obj = feval( name );
end