Merged updates from trunk into stable branch

[feedcatcher.git] / vendor / rails / activesupport / lib / active_support / core_ext / module / delegation.rb

diff --git a/vendor/rails/activesupport/lib/active_support/core_ext/module/delegation.rb b/vendor/rails/activesupport/lib/active_support/core_ext/module/delegation.rb
new file mode 100644 (file)
index 0000000..fb4b5f0
--- /dev/null
+++ b/vendor/rails/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -0,0 +1,121 @@
+class Module
+  # Provides a delegate class method to easily expose contained objects' methods
+  # as your own. Pass one or more methods (specified as symbols or strings)
+  # and the name of the target object as the final <tt>:to</tt> option (also a symbol
+  # or string).  At least one method and the <tt>:to</tt> option are required.
+  #
+  # Delegation is particularly useful with Active Record associations:
+  #
+  #   class Greeter < ActiveRecord::Base
+  #     def hello()   "hello"   end
+  #     def goodbye() "goodbye" end
+  #   end
+  #
+  #   class Foo < ActiveRecord::Base
+  #     belongs_to :greeter
+  #     delegate :hello, :to => :greeter
+  #   end
+  #
+  #   Foo.new.hello   # => "hello"
+  #   Foo.new.goodbye # => NoMethodError: undefined method `goodbye' for #<Foo:0x1af30c>
+  #
+  # Multiple delegates to the same target are allowed:
+  #
+  #   class Foo < ActiveRecord::Base
+  #     belongs_to :greeter
+  #     delegate :hello, :goodbye, :to => :greeter
+  #   end
+  #
+  #   Foo.new.goodbye # => "goodbye"
+  #
+  # Methods can be delegated to instance variables, class variables, or constants
+  # by providing them as a symbols:
+  #
+  #   class Foo
+  #     CONSTANT_ARRAY = [0,1,2,3]
+  #     @@class_array  = [4,5,6,7]
+  #     
+  #     def initialize
+  #       @instance_array = [8,9,10,11]
+  #     end
+  #     delegate :sum, :to => :CONSTANT_ARRAY
+  #     delegate :min, :to => :@@class_array
+  #     delegate :max, :to => :@instance_array
+  #   end
+  #
+  #   Foo.new.sum # => 6
+  #   Foo.new.min # => 4
+  #   Foo.new.max # => 11
+  #
+  # Delegates can optionally be prefixed using the <tt>:prefix</tt> option. If the value
+  # is <tt>true</tt>, the delegate methods are prefixed with the name of the object being
+  # delegated to.
+  #
+  #   Person = Struct.new(:name, :address)
+  #
+  #   class Invoice < Struct.new(:client)
+  #     delegate :name, :address, :to => :client, :prefix => true
+  #   end
+  #
+  #   john_doe = Person.new("John Doe", "Vimmersvej 13")
+  #   invoice = Invoice.new(john_doe)
+  #   invoice.client_name    # => "John Doe"
+  #   invoice.client_address # => "Vimmersvej 13"
+  #
+  # It is also possible to supply a custom prefix.
+  #
+  #   class Invoice < Struct.new(:client)
+  #     delegate :name, :address, :to => :client, :prefix => :customer
+  #   end
+  #
+  #   invoice = Invoice.new(john_doe)
+  #   invoice.customer_name    # => "John Doe"
+  #   invoice.customer_address # => "Vimmersvej 13"
+  #
+  # If the object to which you delegate can be nil, you may want to use the
+  # :allow_nil option. In that case, it returns nil instead of raising a
+  # NoMethodError exception:
+  #
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar
+  #  end
+  #
+  #  Foo.new.zoo   # raises NoMethodError exception (you called nil.zoo)
+  #
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar, :allow_nil => true
+  #  end
+  #
+  #  Foo.new.zoo   # returns nil
+  #
+  def delegate(*methods)
+    options = methods.pop
+    unless options.is_a?(Hash) && to = options[:to]
+      raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, :to => :greeter)."
+    end
+
+    if options[:prefix] == true && options[:to].to_s =~ /^[^a-z_]/
+      raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
+    end
+
+    prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_"
+
+    allow_nil = options[:allow_nil] && "#{to} && "
+
+    methods.each do |method|
+      module_eval(<<-EOS, "(__DELEGATION__)", 1)
+        def #{prefix}#{method}(*args, &block)                           # def customer_name(*args, &block)
+          #{allow_nil}#{to}.__send__(#{method.inspect}, *args, &block)  #   client && client.__send__(:name, *args, &block)
+        end                                                             # end
+      EOS
+    end
+  end
+end