What does :: do?

Question

I have some inherited code that I am modifying. However, I am seeing something strange(to me).

I see some code like this:

::User.find_by_email(params[:user][:email]).update_attributes(:mag => 1)

I have never seen something like this(I am new to Ruby on Rails). What does this do and why doesn't my User.find_by_email(params[:user][:email]).update_attributes(:mag => 1) work? The error says something about the User constant.

I am using Rails 2.3.5 if that helps.

Answer 1

:: is a scope resolution operator, it effectively means "in the namespace", so ActiveRecord::Base means "Base, in the namespace of ActiveRecord"

A constant being resolved outside of any namespace means exactly what it sounds like - a constant not in any namespace at all.

It's used in places where code may be ambiguous without it:

module Document
  class Table # Represents a data table

    def setup
      Table # Refers to the Document::Table class
      ::Table # Refers to the furniture class
    end

  end
end

class Table # Represents furniture
end