Quick-and-dirty class constructor for MATLAB? - oop

Question

I am trying to make MATLAB a bit more usable than it is (for me), and one of the things which I always wanted to fix is a better class constructor. I want to have the following interface:
MyClass.new(some_args).method1;
# instead of classical:
obj = MyClass(some_args);
obj.method1;
I can easily achieve this by defining a static method new:
classdef MyClass
methods
function obj = MyClass(varargin); end
function method1(obj,varargin); end
end
methods (Static)
function obj = new(varargin); obj = MyClass(varargin{:}); end
end
end
But this requires adding such method to all classes, and therefore it is not very elegant/convenient. I thought that I could go around it by defining a common class with the following constructor
classdef CommonClass
methods (Static)
function obj = new(varargin)
# getting name of the current file (Object), i.e. basename(__FILE__)
try clear E; E; catch E, [s, s] = fileparts(E.stack(1).file); end;
# creating object with name $s
obj = eval([s '(varargin{:})']);
end
end
end
classdef MyClass < CommonClass
end
However, this doesn't work because MATLAB calls new() from Object.m, and therefore I get instance of Object instead of MyClass.
Any ideas how I can improve it?
EDIT1:
I would like it to work also for classes created inside other ones:
classdef MyAnotherClass < CommonClass
methods
function obj = MyAnotherClass
child = MyClass.new;
end
end
end
>> MyAnotherClass.new

Answer 1

Personally, I don't see the problem with calling the constructor as is, but if you do want to have it called via new, the getStaticCallingClassName below might be of use to you.
Here's how you'd use it:
classdef CommonClass
methods (Static)
function obj = new(varargin)
%# find out which class we have to create
className = getStaticCallingClassName;
constructor = str2func(sprintf('#%s'className));
%# creating object with name $s
obj = constructor(varargin{:});
end
end
end
classdef MyClass < CommonClass
end
With this, you can call
obj = MyClass.new(input,arguments);
And here's getStaticCallingClassName:
function className = getStaticCallingClassName
%GETSTATICCALLINGCLASSNAME finds the classname used when invoking an (inherited) static method.
%
% SYNOPSIS: className = getStaticCallingClassName
%
% INPUT none
%
% OUTPUT className: name of class that was used to invoke an (inherited) static method
%
% EXAMPLE
%
% Assume you define a static method in a superclass
% classdef super < handle
% methods (Static)
% doSomething
% % do something here
% end
% end
% end
%
% Also, you define two subclasses
% classdef sub1 < super
% end
%
% classdef sub2 < super
% end
%
% Both subclasses inherit the static method. However, you may be
% interested in knowing which subclass was used when calling the static
% method. If you call the subclass programmatically, you can easily pass
% the name of the subclass as an input argument, but you may want to be
% able to call the method from command line without any input and still
% know the class name.
% getStaticCallingClassName solves this problem. Calling it in the above
% static method 'doSomething', it returns 'sub1' if the static method was
% invoked as sub1.doSomething. It also works if you create an instance of
% the subclass first, and then invoke the static method from the object
% (e.g. sc = sub1; sc.doSomething returns 'sub1' if .doSomething calls
% getStaticCallingClassName)
%
% NOTE: getStaticCallingClassName reads the last workspace command from
% history. This is an undocumented feature. Thus,
% getStaticCallingClassName may not work in future releases.
%
% created with MATLAB ver.: 7.9.0.3470 (R2009b) on Mac OS X Version: 10.5.7 Build: 9J61
%
% created by: Jonas Dorn
% DATE: 16-Jun-2009
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% get the last entry of the command line from the command history
javaHistory=com.mathworks.mlservices.MLCommandHistoryServices.getSessionHistory;
lastCommand = javaHistory(end).toCharArray';%'# SO formatting
% find string before the last dot.
tmp = regexp(lastCommand,'(?:=|\.)?(\w+)\.\w+\(?(?:.*)[;,]*\s*$','tokens');
try
className = tmp{1}{1};
catch me
className = [];
end
% if you assign an object, and then call the static method from the
% instance, the above regexp returns the variable name. We can get the
% className through getting the class of xx.empty.
if ~isempty(className)
className = evalin('base',sprintf('class(%s.empty);',className));
end

Answer 2

I could be missing something, but what's wrong with
method1(MyClass(some_args))
? (I use this pattern all the time).