1  module ActiveSupport
   2    module CoreExtensions
   3      module Module
   4        # Encapsulates the common pattern of:
   5        #
   6        #   alias_method :foo_without_feature, :foo
   7        #   alias_method :foo, :foo_with_feature
   8        #
   9        # With this, you simply do:
  10        #
  11        #   alias_method_chain :foo, :feature
  12        #
  13        # And both aliases are set up for you.
  14        #
  15        # Query and bang methods (foo?, foo!) keep the same punctuation:
  16        #
  17        #   alias_method_chain :foo?, :feature
  18        #
  19        # is equivalent to
  20        #
  21        #   alias_method :foo_without_feature?, :foo?
  22        #   alias_method :foo?, :foo_with_feature?
  23        #
  24        # so you can safely chain foo, foo?, and foo! with the same feature.
  25        def alias_method_chain(target, feature)
  26          # Strip out punctuation on predicates or bang methods since
  27          # e.g. target?_without_feature is not a valid method name.
  28          aliased_target, punctuation = target.to_s.sub(/([?!=])$/, ''), $1
  29          yield(aliased_target, punctuation) if block_given?
  30 
  31          with_method, without_method = "#{aliased_target}_with_#{feature}#{punctuation}", "#{aliased_target}_without_#{feature}#{punctuation}"
  32 
  33          alias_method without_method, target
  34          alias_method target, with_method
  35 
  36          case
  37            when public_method_defined?(without_method)
  38              public target
  39            when protected_method_defined?(without_method)
  40              protected target
  41            when private_method_defined?(without_method)
  42              private target
  43          end
  44        end
  45 
  46        # Allows you to make aliases for attributes, which includes
  47        # getter, setter, and query methods.
  48        #
  49        # Example:
  50        #
  51        #   class Content < ActiveRecord::Base
  52        #     # has a title attribute
  53        #   end
  54        #
  55        #   class Email < Content
  56        #     alias_attribute :subject, :title
  57        #   end
  58        #
  59        #   e = Email.find(1)
  60        #   e.title    # => "Superstars"
  61        #   e.subject  # => "Superstars"
  62        #   e.subject? # => true
  63        #   e.subject = "Megastars"
  64        #   e.title    # => "Megastars"
  65        def alias_attribute(new_name, old_name)
  66          module_eval <<-STR, __FILE__, __LINE__ + 1
  67            def #{new_name}; self.#{old_name}; end          # def subject; self.title; end
  68            def #{new_name}?; self.#{old_name}?; end        # def subject?; self.title?; end
  69            def #{new_name}=(v); self.#{old_name} = v; end  # def subject=(v); self.title = v; end
  70          STR
  71        end
  72      end
  73    end
  74  end