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 :to option (also a symbol # or string). At least one method and the :to 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 # # # 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 :prefix option. If the value # is true, 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" # 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]}_" methods.each do |method| module_eval(<<-EOS, "(__DELEGATION__)", 1) def #{prefix}#{method}(*args, &block) #{to}.__send__(#{method.inspect}, *args, &block) end EOS end end end