# Marshaling an object destroys dynamically created methods

**URL:** <https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344>\
**Category:** Ruby\
**Created:** [August 20, 2008, 6:21am UTC](https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344 "2008-08-20T06:21:04Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![lynchnco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c77e96/32.png) [@lynchnco](https://www.ruby-forum.com/u/lynchnco)\
**Post date:** [August 20, 2008, 6:21am UTC](https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344/1 "2008-08-20T06:21:04Z")

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I noticed this this afternoon:  
Unmarshaling a marshaled object, makes all dynamically created methods  
private.

#Here’s a class that dynamically creates the method MyPage#print()  
class MyPage  
def initialize  
MyPage.class\_eval do  
def print  
puts @a  
end  
end  
end  
end

#Test the class  
page = MyPage.new  
page.print #prints nil

#Marshal the object  
File.open(“object.obj”,“w”) do |f|  
Marshal.dump(page, f)  
end

#UnMarshal the object, and try printing again  
page = nil  
File.open(“object.obj”,“r”) do |f|  
page = Marshal.load(f)  
end  
page.print

#gives me:  
#private method `print’ called for #\<MyPage:0x27af394 @a=3\>  
(NoMethodError)

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<div class="post-metadata">

**Author:** ![lynchnco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c77e96/32.png) [@lynchnco](https://www.ruby-forum.com/u/lynchnco)\
**Post date:** [August 20, 2008, 6:39am UTC](https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344/2 "2008-08-20T06:39:02Z")

</div>

From: Patrick Li [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

# I noticed this this afternoon:

# Unmarshaling a marshaled object, makes all dynamically created methods

# private.

check your ruby version, pls

class MyPage  
def initialize  
MyPage.class\_eval do  
def print  
puts @a  
end  
end  
end  
end  
#=\> nil

#Test the class  
page = MyPage.new  
#=\> #MyPage:0x28d7154  
page.print #prints nil  
nil  
#=\> nil

#Marshal the object  
File.open(“object.obj”,“w”) do |f|  
Marshal.dump(page, f)  
end  
#=\> #\<File:object.obj (closed)\>

#UnMarshal the object, and try printing again  
page = nil  
#=\> nil  
File.open(“object.obj”,“r”) do |f|  
page = Marshal.load(f)  
end  
#=\> #MyPage:0x28c1980  
page.print  
nil  
#=\> nil

[RUBY\_VERSION,RUBY\_PATCHLEVEL,RUBY\_RELEASE\_DATE,RUBY\_PLATFORM]  
#=\> [“1.8.6”, 286, “2008-08-08”, “i386-mswin32”]

kind regards -botp

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<div class="post-metadata">

**Author:** ![lynchnco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c77e96/32.png) [@lynchnco](https://www.ruby-forum.com/u/lynchnco)\
**Post date:** [August 20, 2008, 10:15am UTC](https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344/3 "2008-08-20T10:15:09Z")

</div>

I’m not in a position to test, but it looksnto me like the method  
print simply isn’t created on the unMarshaled object. Since the  
methods in Kernel are included in Object as private methods, you get  
the same error message from Object.new.print or Object.new.throw. I’m  
not familiar with Marshaling at all, but this may help you debug. Good  
luck 🙂

–  
Mikael H©ªilund, CTO of [Meta.io](http://Meta.io)

On Aug 20, 2008, at 6:17 AM, Patrick Li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

<div class="post-metadata">

**Author:** ![lynchnco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c77e96/32.png) [@lynchnco](https://www.ruby-forum.com/u/lynchnco)\
**Post date:** [August 21, 2008, 12:45pm UTC](https://www.ruby-forum.com/t/marshaling-an-object-destroys-dynamically-created-methods/146344/4 "2008-08-21T12:45:14Z")

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2008/8/20 Patrick Li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> I noticed this this afternoon:  
> Unmarshaling a marshaled object, makes all dynamically created methods  
> private.

Patrick, that’s not correct. Classes and methods aren’t changed upon  
marshalling.

> #Here’s a class that dynamically creates the method MyPage#print()  
> class MyPage  
> def initialize  
> MyPage.class\_eval do  
> def print  
> puts @a  
> end  
> end  
> end  
> end

This creates a MyPage#print method for _all_ MyPage instances as soon  
as the first instance is created.

> #Test the class  
> page = MyPage.new

Here the MyPage#print method is created.

> page.print #prints nil

As expected.

> #Marshal the object  
> File.open(“object.obj”,“w”) do |f|  
> Marshal.dump(page, f)  
> end

Maybe you should stop Ruby at this point, see below. If you just  
continue with the following code, you don’t get the output you’ve  
shown, as botp already wrote.

> #UnMarshal the object, and try printing again  
> page = nil  
> File.open(“object.obj”,“r”) do |f|  
> page = Marshal.load(f)  
> end  
> page.print
> 
> #gives me:  
> #private method `print’ called for #\<MyPage:0x27af394 @a=3\>  
> (NoMethodError)

No, you don’t get this error. See botp’s example.

If you stop Ruby at the point shown above, then start a new session,  
define the MyPage class as above, and then run the unmarshalling code,  
then it’s normal and expected that you get a NoMethodError.  
Unmarshaling an object doesn’t call it’s class’ #initialize method, so  
the new method MyPage#print never is defined in the second Ruby  
session. That’s why you are calling the private method Kernel#print  
and get the error.

Regards,  
Pit