# Scope resolution operator **URL:** \ **Category:** Ruby\ **Created:** [January 25, 2009, 1:21am UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570 "2009-01-25T01:21:17Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![dewie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ac8455/32.png) [@dewie](https://www.ruby-forum.com/u/dewie)\ **Post date:** [January 25, 2009, 1:21am UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570/1 "2009-01-25T01:21:17Z")
(The code I will demonstrate is Rails-based, but the question is Ruby-based.) I’m familiar with the following: ActiveRecord::Base Basically says, look inside ActiveRecord for a class or module named Base. But what about the following: ::Attachment Does that basically say, no matter what scope you are in, jump to the highest level to look for the class or module named Attachment? The following code only works when I prefix the Attachment class with :: has\_one :attachment, :as =\> :attachable, :class\_name =\> ‘::Attachment’ def assign\_attachment=(attachment\_id) self.attachment = ::Attachment.find(attachment\_id) end ---
**Author:** ![dewie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ac8455/32.png) [@dewie](https://www.ruby-forum.com/u/dewie)\ **Post date:** [January 25, 2009, 9:15am UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570/2 "2009-01-25T09:15:11Z")
Alle domenica 25 gennaio 2009, Daniel W. ha scritto: > ::Attachment > Does that basically say, no matter what scope you are in, jump to the > highest level to look for the class or module named Attachment? According to “The Ruby P.ming Language”, ::Something is a shortcut for Object::Something. The idea is that ::Something should look up a constant called Something in the global scope, but since ruby doesn’t truly have a global scope, it looks it up in the Object class, which is the nearest thing in ruby to a global scope. > The following code only works when I prefix the Attachment class with :: > > has\_one :attachment, :as =\> :attachable, :class\_name =\> ‘::Attachment’ > > def assign\_attachment=(attachment\_id) > self.attachment = ::Attachment.find(attachment\_id) > end Not knowing rails, I can’t say much on this. However, if it works with ::Attachment and doesn’t work with Attachment, the only thing I can think of is that you have two constants called Attachment: one at global level, which is the one you need here, and another at a more local level which is the one you get without the :: I hope this helps Stefano ---
**Author:** ![dewie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ac8455/32.png) [@dewie](https://www.ruby-forum.com/u/dewie)\ **Post date:** [January 25, 2009, 9:54am UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570/3 "2009-01-25T09:54:21Z")
Stefano C. wrote: > Not knowing rails, I can’t say much on this. However, if it works with > ::Attachment and doesn’t work with Attachment, the only thing I can > think of > is that you have two constants called Attachment: one at global level, > which > is the one you need here, and another at a more local level which is the > one > you get without the :: You may not be familiar with Rails but you certainly know Ruby. That is exactly the case. The Paperclip module defines an Attachment class, methods of which I am using in my own Attachment class. Talk about a naming conflict. Grr… Thanks for the reply Stefano, it’s helped a lot. ---
**Author:** ![dewie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ac8455/32.png) [@dewie](https://www.ruby-forum.com/u/dewie)\ **Post date:** [January 27, 2009, 2:55pm UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570/4 "2009-01-27T14:55:36Z")
2009/1/25 Stefano C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > But what about the following: > > ::Attachment > > Does that basically say, no matter what scope you are in, jump to the > > highest level to look for the class or module named Attachment? > > According to “The Ruby P.ming Language”, ::Something is a shortcut for > Object::Something. The idea is that ::Something should look up a constant > called Something in the global scope, but since ruby doesn’t truly have a > global scope, it looks it up in the Object class, which is the nearest thing > in ruby to a global scope. As an illustration: 14:52:57 ~$ ruby -e ‘puts Object.constants.sort’ ARGF ARGV ArgumentError Array Bignum Binding Class Comparable Continuation Data Dir ENV EOFError Enumerable Errno Exception FALSE FalseClass File FileTest Fixnum Float FloatDomainError GC Hash IO IOError IndexError Integer Interrupt Kernel LoadError LocalJumpError Marshal MatchData MatchingData Math Method Module NIL NameError NilClass NoMemoryError NoMethodError NotImplementedError Numeric Object ObjectSpace … You see all the globally scoped classes (later on there will be String etc.). Notice also the nice element of self referentiality. 🙂 Kind regards robert ---
**Author:** ![dewie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ac8455/32.png) [@dewie](https://www.ruby-forum.com/u/dewie)\ **Post date:** [January 28, 2009, 8:07pm UTC](https://www.ruby-forum.com/t/scope-resolution-operator/158570/5 "2009-01-28T20:07:54Z")
- Stefano C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (2009-01-25) schrieb: > According to “The Ruby P.ming Language”, ::Something is a shortcut for > Object::Something. The idea is that ::Something should look up a constant > called Something in the global scope, but since ruby doesn’t truly have a > global scope, it looks it up in the Object class, which is the nearest thing > in ruby to a global scope. ,---- | $ cat /tmp/scope.rb | Something = “blubb” | | module Bla | class Object | Something = “crazy” | end | | puts ::Something | puts Object::Something | end | $ ruby /tmp/scope.rb | blubb | crazy | $ `---- mfg, simon … l