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
#
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
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
