field ordering in octave's save/load

[Sergei Steshenko]

--- On Tue, 3/3/09, Gunnar Rätsch <Gunnar.Raetsch at tuebingen.mpg.de> wrote:

> From: Gunnar Rätsch <Gunnar.Raetsch at tuebingen.mpg.de>
> Subject: field ordering in octave's save/load
> To: bug at octave.org
> Date: Tuesday, March 3, 2009, 12:39 PM
> Dear octave team,
> 
> I've been using octave a lot recently and am really
> happy with its  
> recent progress. Thanks a lot for your efforts!
> 
> I came across one issue today, which isn't really a
> bug, but just a  
> different behaviour compared to matlab, which you may want
> to fix (at  
> least it would help me quite a bit).
> I've noticed that when structures are saved and then
> loaded again in  
> octave, then the fields are alphabetically sorted. This is
> not the  
> case in matlab.
> I had a piece of code that depended on the ordering of
> these fields  
> and therefore the octave code failed, while the matlab code
> worked  
> just fine (this was a difficult-to-find bug).
> 
> What do you think? Do you intend to change the code such
> that the  
> field order is preserved?
> 
> Thanks a lot in advance,
> 
> Gunnar
> 

IIRC, structs are hashes, struct fields are hash keys, and typically hash
keys order cannot be relied upon, i.e. one has to use a special (not the
simplest) implementation of hashes in order to preserve hash keys order.

So, does Matlab promise hash keys order in your scenario ?

If yes, then it's a bug in 'octave', if not - then it's a bug in your code
- it relies on an undocumented feature.

Regards,
  Sergei.