[wxruby-users] use of Marshal with wxruby classes

[Alex Fenton]

Robert Anderson wrote:
> Is it possible to use Marshal with wxruby classes to serialize an 
> application's state?
>
> I tried a minimal example of simply serializing a minimal frame 
> object, and I get the error "no marshal_dump is defined for class 
> MinimalFrame".
>
> I don't fully understand this because I also tried another minimal 
> example of dumping a class which did not defined a marshal_dump, and 
> it worked fine.  Is there some reason this has been disabled in wxruby 
> classes?  Sorry, I picked up ruby a few days ago so I may be missing 
> something obvious.

It's not completely obvious, but I'm fairly sure what's happening is 
this: Marshal is able to store ordinary ruby objects that are composed, 
in the end, of core ruby types, like Float, Fixnum, String, Hash etc. So 
if you write any class just in ruby, Marshal can serialise its instances.

Objects like a Wx::Frame, or any other ruby object that comes from a 
ruby C extension is different. It's a wrapper or pointer to compiled 
code (a C++ object in wxRuby). Ruby can't serialise and restore such 
objects without extra information.

Not sure why you'd want to serialise a Wx::Frame. If you're interested 
in storing and restoring the size, position or layout of a Frame between 
runs, just store that information and a hash and serialise it, and then 
when the "same" window is re-opened, Marshal.load the hash and restore 
the settings. The first few methods in this real-life app do this sort 
of thing:

http://weft-qda.rubyforge.org/svn/trunk/weft-qda/lib/weft/wxgui/inspectors.rb

hth
alex