How to convert multi-line module/class into single line with double colons(::) in Ruby?

Question

This is an example of a class I have:

module Project
  module Alert
    class NotifyService
    end
  end
end

Now I want to replace that with colons(::).

Option 1:

module Project::Alert::NotifyService
end

Option 2:

class Project::Alert::NotifyService
end

I don't want these to happen:

# NotWanted A
class Project
  class Alert
    class NotifyService
    end
  end
end

# or
# NotWanted B

module Project
  module Alert
    module NotifyService
    end
  end
end

Which is the equivalent of the original one? And is there a way to tell that?

Answer 1

the second one, but only if the parent modules actually exist before you start:

your original:

jonathan@ADAMS-3DJ5PW2:~$ irb
2.5.8 :001 > module Project
2.5.8 :002?>     module Alert
2.5.8 :003?>         class NotifyService
2.5.8 :004?>           end
2.5.8 :005?>       end
2.5.8 :006?>   end
 => nil 
2.5.8 :007 > Project.new
Traceback (most recent call last):
        2: from /home/jonathan/.rvm/rubies/ruby-2.5.8/bin/irb:11:in `<main>'
        1: from (irb):7
NoMethodError (undefined method `new' for Project:Module)
2.5.8 :008 > Project::Alert.new
Traceback (most recent call last):
        2: from /home/jonathan/.rvm/rubies/ruby-2.5.8/bin/irb:11:in `<main>'
        1: from (irb):8
NoMethodError (undefined method `new' for Project::Alert:Module)
2.5.8 :009 > Project::Alert::NotifyService.new
 => #<Project::Alert::NotifyService:0x000055a483abd808> 
2.5.8 :010 > exit

your second (without definition):

jonathan@ADAMS-3DJ5PW2:~$ irb
2.5.8 :001 > class Project::Alert::NotifyService
2.5.8 :002?>   end
Traceback (most recent call last):
        2: from /home/jonathan/.rvm/rubies/ruby-2.5.8/bin/irb:11:in `<main>'
        1: from (irb):1
NameError (uninitialized constant Project)
Did you mean?  Object
2.5.8 :003 > exit

your second, with the addition of module definitions first:

jonathan@ADAMS-3DJ5PW2:~$ irb
2.5.8 :001 > module Project
2.5.8 :002?>   module Alert
2.5.8 :003?>     end
2.5.8 :004?>   end
 => nil 
2.5.8 :005 > class Project::Alert::NotifyService
2.5.8 :006?>   end
 => nil 
2.5.8 :007 > Project.new
Traceback (most recent call last):
        2: from /home/jonathan/.rvm/rubies/ruby-2.5.8/bin/irb:11:in `<main>'
        1: from (irb):7
NoMethodError (undefined method `new' for Project:Module)
2.5.8 :008 > Project::Alert.new
Traceback (most recent call last):
        2: from /home/jonathan/.rvm/rubies/ruby-2.5.8/bin/irb:11:in `<main>'
        1: from (irb):8
NoMethodError (undefined method `new' for Project::Alert:Module)
2.5.8 :009 > Project::Alert::NotifyService.new
 => #<Project::Alert::NotifyService:0x00005604a90e79b0> 
2.5.8 :010 > exit