ActiveRecord::Base

rubyonrails-talk
#1

Hello all,

      What is significance of :: in ActiveRecord::Base.

What is difference between ::String.new and String.new

Thank you,
Praveen

#2

::String means explicit root namespace.

So if you have something like
module MyNamespace
class String
…
end
end

MyNamespace::String will be your own class, while ::String will still be the original string class defined by Ruby. If you just type String, it’ll find the closest matching namespace, so if you call String.new from within MyNamespace, it’ll return MyNamespace::String, while if you call String.new from outside MyNamespace, it’ll call the default Ruby string. Writing ::String means you explicitly want the default Ruby string, even if you call it from inside MyNamespace.

#3

Good question!

Using :: you have access to the class inside the module. Module can nest
another modules and so on. :: its a namespace resolution operator.

Call ::String.new inside some module back you to top-level namespace
(outside the module)

Here is examples

class String
def initialize
   puts "im string outside module"
end
end

module ActiveRecord
  module AnotherModule
  end

  class String
   def initialize
     puts "im string inside module"
   end
  end

  class Base
   def initialize
    ::String.new
    String.new
   end
  end
end

Here are results from IRB:

1.9.3-p392 :021 > ActiveRecord::Base.new
im string outside module
im string inside module
=> #<ActiveRecord::Base:0xa024fb8>
1.9.3-p392 :022 > ActiveRecord::String.new
im string inside module
=> #<ActiveRecord::String:0xa023168>