clone & singleton classes

[marcandre]

If a specific Nokogiri::HTML::Document extends a module M, a clone of that document won't.

I expected otherwise, since in Ruby all builtin classes, as well as user created classes will copy the singleton_class when cloning.

Thakns!

require 'nokogiri'
require 'open-uri'

module M; def foo; end end

doc = Nokogiri::HTML(open('http://www.google.com/search?q=tenderlove'))
doc.extend M
doc.clone.respond_to? :foo # => false, should be true

[flavorjones]

Fair enough, will fix.

[flavorjones]

Well, here's a question for you: Nokogiri documents already follow "nontraditional" clone/dup semantics by copying the underlying document tree.

So: can you explain your use case for extending an object and then cloning it? I'm just trying to wrap my head around how this idiom is being used with Nokogiri objects.

[marcandre]

I coded up some parsing methods that apply for any web site; the methods are in a module which I include in Nokogiri document. Later on I needed some custom parsing for some specific domains. The easy way out was to extend the document with the module specific for the domain. Different parsing need to be done and tend to be destructive so I cloned the document before calling the different parsing methods.

There are other solutions; I can subclass Document, have the methods be module functions and pass the document, create a sort of delegate class and sub class that, extend all clones, etc...

But since cloning should copy the singleton class, I thought you might want to fix it :-)
It's clearly not a big priority!

[flavorjones]

Thanks for going into detail. I'm always interested in what people are doing with nokogiri (well, almost always ;)).

LIke I said, this is a fair enough request, I don't have a problem with it. We'll schedule work, and probably target 1.5.

[flavorjones]

Description of differences between dup and clone:

• https://stackoverflow.com/questions/10183370/whats-the-difference-between-rubys-dup-and-clone-methods
• https://ruby-doc.org/core-2.5.1/Object.html#method-i-dup-label-on+dup+vs+clone
• https://blog.appsignal.com/2019/02/26/diving-into-dup-and-clone.html (2019)

[flavorjones]

Picked up this work yesterday, see progress in #3117

"Better late than never" as they say 😅