Saving all instance variables of an object

abakobo

Hi

I wonder if i can create functions that load/saves all the instance variables of an object in a convenient way that could be used after for any object... (or/and if it has been done already (couldn't find it on Google..))
I've just started to use .each and other ruby nice stuffs so i'm a bit confused and don't know what is actualy possible.

Saving


def Save_Obj_Inst_Vars(FILENAME,object)

 fileout = File.open FILENAME, "w+"

 fileout.puts object.class #write the class type to check compatibility when loading

 object.instance_variables.each do |the_var|
  fileout.puts the_var.class
  fileout.puts the_var
 end
 fileout.close

end

Loading


def Load_Obj_Inst_Var(FILENAME,object)

 filein = File.open FILENAME, "r"
 filein.rewind #needed if file was not closed?

 class_type=filein.gets 

 if class_type==object.class 
  object.instance_variables.each do |the_var|
   typ=filein.gets
   val=filein.gets
   case typ
    when 'int'
     val=val.to_i
    when 'float'
     val=val.to_f
    when 'bool'
     val=val.to_b
    when 'string'
     # already string? do nothing?
   end
   the_var=val
  end
 else
  puts 'bad type!'
 end

 filein.close

end

Do I have a chance to get something like that working? will the instance_variables array be in the same order all the time with the ".instance_variables" method so I can load it safely? What would be a classy ruby code style to do this? Can I differentiate public and private instance variable (the ones with att_accessor)?

many thanks

ako

Dan Rathbun

@abakobo said:

Do I have a chance to get something like that working?

(1) Always use the block form of File.open so the file is automatically closed.

The names returned by the array have "@" at the beginning of them.

In Ruby 1.8.x, the members are all strings, in Ruby 2.x the members are all symbols.

If it were me, and I was not going to use Marshal, I'd use a comma separated format:
puts "%s,%s,%s" % [ the_var.to_s, eval(the_var.to_s).class.name, eval(the_var.to_s).to_s.inspect ]

Right now I am just using Sketchup::write_default() and Sketchup::read_default() to store and recall plugin variables.

But there are library utilities like PStore:
http://phrogz.net/ProgrammingRuby/lib_standard.html#PStore

@abakobo said:

... will the instance_variables array be in the same order all the time with the ".instance_variables" method so I can load it safely?

No, do not count on any particular order. Always refer to variables by their reference name.

But I do not understand what you mean by "the instance_variables array" as opposed to the ".instance_variables method". The former (array) is returned by the introspection method, and it is an array of string or symbol names of the variables, not the objects that the variables reference.

@abakobo said:

What would be a classy ruby code style to do this?

There is [url=http://ruby-doc.org/core-2.0.0/Marshal.html:1ko8kfu8]Marshal[/url:1ko8kfu8].
You can define marshal_dump and marshal_load methods for your classes to leverage this feature.

@abakobo said:

Can I differentiate public and private instance variable (the ones with att_accessor)?

There really is no such thing as private instance variables.

But you can look through an array returned by instance_methods() to see if there is a method with the same name as a given instance variable. (But that is not an absolute assurance that the method was created with the attribute methods.)

The methodname strings or symbols will not have the "@" symbol at the beginning.
So you'll need to strip the "@" off the var name for comparison:
if obj.instance_methods().find {|meth| the_var.to_s[1..-1] == meth.to_s }
If there is an accessor method, it will be returned and eval true by if, but if not in the array, nil is returned by find, and eval'd as false.

abakobo

Thank you very much!

This helped me a lot and I have ALL the infos I needed!

ako

abakobo

Hi

I decided to use Marshal as I suppose I won't do better! (though it's version dependent and has some security issues)

I found some code examples modified and ran it... cool stuff. But there are two things I don't understand in the code I copied!


class MyObject 
	
	def initialize(value)  
		@value = value 
		@arr= [4,5,6]
	end  
	attr_accessor ;value, ;arr
	
	def incr
		@value=@value+1
	end
	
end  


obj=MyObject.new(99)

file_name=UI.savepanel("Save","",".oob")

File.open(file_name, 'w+') do |f|
	Marshal.dump(obj, f) 
end


File.open(file_name) do |f|  
	@obj2 = Marshal.load(f)  
end  

obj3=@obj2.clone
obj3.incr
puts obj3.value,obj3.arr

Why must I use @ or $ for my obj2?

And why the code below doesn't close the file in comparaison to the one above. Is that the "block form" advised in Dan's post? I miss the mechanics of that "do ||" statement, I tought it was just a looping tool. ---> I read this now: http://blog.rubybestpractices.com/posts/gregory/009-beautiful-blocks.html


f=File.open(file_name, 'w+')
puts f
Marshal.dump(obj, f)

#need f.close!

Thanks a lot for your answers!

ako

slbaumgartner

@abakobo said:

Why must I use @ or $ for my obj2?
[

These prefixes are part of the names of variables. They tell Ruby what scope the variables belong to (@ for attributes of objects, $ for globals - there is also @@ for class variables). Variables without one of these leading characters are local to the code scope where they appear.

thomthom

@slbaumgartner said:

They tell Ruby what scope the variables belong to (@ for attributes of objects, $ for globals

And for the record - global variables should be avoided. In Extension Warehouse they are an immediate rejection.

Dan Rathbun

@thomthom said:

And for the record - global variables should be avoided. In Extension Warehouse they are an immediate rejection.

And yet.. the global objectspace is still cluttered with global variables created by SketchUp Team extensions!

Many of these are for LanguageHandler instances that are no longer needed once the Preferences UI strings have been loaded, or a local extension hash loaded with strings.

thomthom

Yea - there's a need for a cleanup for the old SketchUp extensions.

abakobo

I tried to save an object containing an SKUI window object (using marshal) and had a bad type error... I suppose it's not possible to save an SKUI window with marshal due to it's limitations:

*Marshal can't dump following objects:

anonymous Class/Module.

objects which related to its system (ex: Dir, File::Stat, IO, File, Socket and so on)

an instance of MatchData, Data, Method, UnboundMethod, Proc, Thread, ThreadGroup, Continuation

objects which defines singleton methods*

I did it manualy this time but wonder if there's something similar to Marshal with what I would be able to save objects containing SKUI windows for later use.

I remeber i saw somthing with a name looking like "yalm"..
Would Pstore do it?

Many Thanks

ako

thomthom

Classes needs to implement support for marshalling. In the case of SKUI the Window class holds on to references to UI::WebDialog - which cannot be serialized. This also is also the case for Sketchup::Entity derived classes.

Btw, why are you trying to marshall a SKUI Window? Are you trying to save the window position?
Or are you trying to save the whole state of it - including HTML content and session?

abakobo

I'm trying to save all the .visible? .caption(for lbls) and .value(for inputs) for now.

I would like to create a window where there's a "add item" on the window that add a SKUI_group on the window corresponding to the new item...
My object have only two instance variables for now, the number of items(an int) and the SKUI window.

For the non customisable plugin I could save the .visible? .caption and .value by listing them manualy in my Save method but with a customizable window it would probably be painful...

thanks for your answers
AND THANKS A LOT FOR SKUI (sorry for shouting but i really mean it)

P.S. I noticed a little bug: I have to initialise myself the .visible of each visible unmodified SKUI items before saving them because it was returning nil with the .visible? method if .visible= was never used.

thomthom

@abakobo said:

P.S. I noticed a little bug: I have to initialise myself the .visible of each visible unmodified SKUI items before saving them because it was returning nil with the .visible? method if .visible= was never used.

Hmm... Could you file this bug in the GitHub repo with a small code snippet?

abakobo

I never did that but will learn how to.
Glad to participate...

abakobo

Bug posted in the GitHub Issues field!