Re: Gorm - error when saving previous version (Gworkspace)

[Riccardo Mottola]

Hi,

On 05/25/12 19:51, Fred Kiefer wrote:
> I looked into your problem more deeply and there were two issues 
> blocking you. One was the change Richard made in the way we store the 
> item count of an array in archives. Richard improved on that an now 
> archives store this count in a forward compatible way in most cases, 
> this means old code will be able to read arrays in archives written by 
> newer code.
> The other issues hasn't been resolved and is unlikely to get resolved. 
> In the last release we changed the way some classes get archived. This 
> has happened for almost all gui releases over the last years and there 
> isn't much we can do about it. We try to implement the new archiving 
> code in a way that allows us to read old archives, but there is no way 
> to allow old code to read newer archives, when the format changes.
> Now the simplest solution for you would be to switch over to keyed 
> archives, in this case from Gorm to NIB files. This format is backward 
> and forward compatible most of the time and for this reason should be 
> preferred over non-keyed archives.
This essentially means that the option Greg has given in Gorm to save 
old file formats is unreliable as soon as there is a bigger change in 
the classes.
> If this isn't an option for you, your could try to build a hybrid 
> version of archiving for the classes that are needed for you specific 
> Gorm files. That is, you move the -encodeWithCoder: back to the last 
> version and keep the -initWithCoder: method on the new state. This 
> requires that you find all the classes where this is needed and is is 
> also a bit dangerous, as you will write out the objects with the wrong 
> version number if you don't change that number as well.
> If you are very sure that your only problem are the unsigned/signed 
> changes that Sebastian made a while ago, then there is another option, 
> you could remove the sign check from the base code, or rather make it 
> a warning. (This is in NSUnarchiver.m in the function typeCheck) This 
> may even be a change we could keep. But don't expect this to resolve 
> all your issues with forward compatibility. For example NSTableColumn 
> and NSTextView were also changed in a incompatible way. If I remember 
> correctly, this was to fix bugs that you reported.
I transformed the exception in a NSLog() and recompiled a base 1.24 
installation with only that change, then I did run Gorm using that base 
and the only warning I get (except the version number) is that signed 
vs. unsigned and the gorm file opens fine. I resaved it. It seems to 
work and essentially for now.

Riccardo