Hi, i spent a little time with the problem i had some time ago, in effect there is a problem with bindings mechanism in MacRuby 0.6 : - create a new MacRuby Document based project - MyDocument.nib create a new ObjectController binded with File's Owner Content, model key path "dummy" create a new text field binded with ObjectController selection, model key path "name" - MyDocument.rb class MyDocument < NSDocument attr_accessor :dummy def init super setDummy({"name"=>"dummy"}) puts "in init class of Hash is : #{@dummy.class.ancestors}" return self end def windowNibName 'MyDocument' end # Document data representation for saving (return NSData) def dataOfType(type, error:outError) puts "in save class of Hash is : #{@dummy.class.ancestors}" return true end # Read document from data (return non-nil on success) def readFromData(data, ofType:type, error:outError) return true end # Return lowercase 'untitled', to comply with HIG def displayName fileURL ? super : super.sub(/^[[:upper:]]/) {|s| s.downcase} end end bindings works, but when i try to save the document... in init class of Hash is : [Hash, NSMutableDictionary, NSDictionary, Enumerable, NSObject, Kernel] in save class of Hash is : [#<Class:0x200577420>, Hash, NSMutableDictionary, NSDictionary, Enumerable, NSObject, Kernel] of course if i try to serialize the object i obtain : `fileWrapperOfType:error:': can't dump anonymous class #<Class:..........> (TypeError) if i remove the bindings with text field all works again...well i mean no data in it, but at least the class of object remain the same au contraire in MacRuby 0.5 all works fine in init class of Hash is : [NSMutableDictionary, NSDictionary, Enumerable, NSObject, Kernel] in save class of Hash is : [NSMutableDictionary, NSDictionary, Enumerable, NSObject, Kernel] Thanks for any help and workaround Ciao