vendor/rails/activesupport/lib/active_support/core_ext/module/aliasing.rb

   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
  68           def #{new_name}?; self.#{old_name}?; end
  69           def #{new_name}=(v); self.#{old_name} = v; end
  70         STR
  71       end
  72     end
  73   end
  74 end