Re: OOP load update

[Robert T. Short]

John W. Eaton wrote:
> On  5-May-2009, Robert T. Short wrote:
>
> | MATLAB actually can reconstruct all of the 
> | fields of the underlying struct from the mat file, but it is not able to 
> | reconstruct inheritance from the mat file.  Calling the constructor 
> | seems like a natural way to do it, but MATLAB doesn't seem to ever call 
> | the constructor when loading from a mat file. 
>
> Are you sure about that?  Try creating and saving an object of a class
> then make the constructor for that class unavailable in smoe way
> (rename the @NAME directory that contains the constructor, for
> example).  Then restart Matlab and try loading the file.  Does it
> complain about not being able to find the constructor?  Or that it
> can't create the class, so it is converting it to a structure instead?
>   
Not 100%, but reasonably.  I haven't tried what you said, but I did (a) 
put a breakpoint in the constructor and (b) put some output statement in 
the constructor, and (c) making a constructor that failed without an 
argument.  None of these things happen.  I have thought of some more 
conclusive experiments and will try them.

I need to experiment more just to try to characterize this thing.  Right 
now octave works pretty much just like MATLAB.  If you have a class 
FooBar that has inheritance and do

> fubar=FooBar()
> save foobarfile fubar
> exit

(start {MATLAB,octave} again)
> load foobarfile
error:  (some error message about not being able to do this)

but if you do
> FooBar()
> load foobarfile

everything works.


> | In order to load a class with parent classes, you first need to 
> | instantiate an object from the class constructor and then load the mat 
> | file.  This is now the way things work in octave, but I have been 
> | thinking about invoking the class constructor to fill in the class 
> | structure.  As long as the constructor doesn't require arguments it 
> | should work, but I haven't really thought it out that far yet.
>
> It should not be necessary to call the constructor unless an object of
> the class has not yet been created at the point where you need to
> know something about the class layout.
>   
See the example above for what I meant.  If you save a class in a file, 
exit {MATLAB,octave} you have to instantiate an object before the load 
will work.  If I called the class constructor it would work fine, but if 
the constructor HAD to have an argument, it would fail.  Then you would 
still have to instantiate an object.  On the other hand, if there is 
already an entry in the examplar table, there is no reason to do any of 
the above.  I think that is what I do - This makes me think that I had 
best have another look, but I think this is what I do.

I think this is really quite a good approach and will probably play with 
this.

Bob
--
Robert T. Short, Ph.D.
PhaseLocked Systems