Re: OOP and load/save

[Robert T. Short]

John W. Eaton wrote:
> On 23-Apr-2009, Judd Storrs wrote:
>
> | ??? Error using ==> class
> | Number of fields for class Foo cannot be changed without clear classes.
>
> What if you just change the name of a field, but leave the number of
> fields the same?  Does that also generate an error (I hope the answer
> is yes).
>
> |     CLEAR CLASSES is the same as CLEAR ALL except that class definitions
> |     are also cleared. If any objects exist outside the workspace (say in
> |     userdata or persistent in a locked m-file) a warning will be issued and
> |     the class definition will not be cleared. CLEAR CLASSES must be used if
> |     the number or names of fields in a class are changed.
>
> Ah, OK.  So we need to cache the fields (or just number of fields?)
> the first time a constructor is called, and compare field names on all
> subsequent constructor calls.  I guess I can add that feature if
> someone else doesn't get to it before me.  If anyone does decide to
> work on that, then please let me know.
>
> Thanks,
>
> jwe
>
>
>   
OK.  I tried another experiment. 

If I create a class and save it, then "clear classes", the class will 
"load" just fine.

If I exit MATLAB and then try to load the class from the file I get the 
same error that Judd saw.

Ergo, it appears that MATLAB stores the class structure even through a 
clear classes command.  MATLAB does seem to keep track of both the 
number and names of fields.


Do we really need to worry about converting to a structure?  MATLAB does 
it, but that seems pretty useless to me.  Maybe just issue an error.  
Although, perhaps if we derived "octave_class" from "octave_struct", it 
wouldn't be too hard?  That would also take care of some of the "FIXME" 
items you have in ov_class.cc where code is the same between the two files.


I am perfectly willing to work on this since I have already made some 
changes here, but I am kind of slow - normally I can only do this for a 
few hours on the weekends.  I agree that there will be some surgery so I 
would like to discuss major changes before I make them. 

Bob