@Matt – thanks for the clarification

So if your Widgets class had a varargin input for example then when you try

array(9)=Widgets('param');

will call the constructor passing ‘param’ in varargin{1} for the first constructor but then passes in an empty varargin for the next
So the moral I think is to have a no-parameter constructor defined if you are going to use this.

At least that’s the way it seems to work on my R2012b
Cheers

Matt

A small addition:
matlab.mixin.Copyable can also be used for deep copies by overloading the copyElement method as described in the documentation.
Thanks for clearing up that when it was added!

Thanks for mentioning this, matlab.mixin.Copyable can indeed be useful for fast shallow copies, in cases that do not require deep copies. And yes, it was indeed added in R2011a.

Readers interested in object copying might find the following discussion interesting: https://www.mathworks.com/matlabcentral/newsreader/view_thread/257925

Instead of a pool of objects I store only one object and create as many copies as I need when I need them. I haven’t analyzed if a factory approach would be faster though…

@Andrew – I could indeed make getInstance() Static+private (no need to make it hidden), but then I’d need to call it via the Widgets. prefix in pull()/recycle():

obj = Widgets.getInstance();

There’s also the small matter of performance – I believe that calling a sub-function as in my implementation is slightly faster than a class method invocation.

Not major reasons, I admit. There’s a lot of personal taste that goes into such implementations, and there are of course other good implementations. I’ve lost count of the number of singleton implementations I’ve seen over the years. It’s one of those classes that every newbie gets to program as an exercise, and doesn’t know that he got it wrong until he’s shown his/her errors in a technical job interview. Hopefully, my implementation doesn’t fall into this latter category…

As for not making Widgets Sealed, I see no reason to prevent sub-classes from reimplementing the pool differently. For example, instead of retrieving the last-recycled object, retrieving the oldest one in the pool.