forwardable.rb - $Release Version: 1.1$ $Revision: 27967 $ by Keiju ISHITSUKA(firstname.lastname@example.org)
original definition by delegator.rb
Revised by Daniel J. Berger with suggestions from Florian Gross. Documentation by James Edward Gray II and Gavin Sinclair
This library allows you delegate method calls to an object, on a method by method basis.
Be advised, RDoc will not detect delegated methods.
forwardable.rb provides single-method delegation via the def_delegator() and def_delegators() methods. For full-class delegation via DelegateClass(), see delegate.rb.
Forwardable makes building a new class based on existing work, with a proper interface, almost trivial. We want to rely on what has come before obviously, but with delegation we can take just the methods we need and even rename them as appropriate. In many cases this is preferable to inheritance, which gives us the entire old interface, even if much of it isn't needed.
class Queue extend Forwardable def initialize @q = [ ] # prepare delegate object end # setup preferred interface, enq() and deq()... def_delegator :@q, :push, :enq def_delegator :@q, :shift, :deq # support some general Array methods that fit Queues well def_delegators :@q, :clear, :first, :push, :shift, :size end q = Queue.new q.enq 1, 2, 3, 4, 5 q.push 6 q.shift # => 1 while q.size > 0 puts q.deq end q.enq "Ruby", "Perl", "Python" puts q.first q.clear puts q.first
2 3 4 5 6 Ruby nil
SingleForwardable can be used to setup delegation at the object level as well.
printer = String.new printer.extend SingleForwardable # prepare object for delegation printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts() printer.puts "Howdy!"
Also, SingleForwardable can be use to Class or Module.
module Facade extend SingleForwardable def_delegator :Implementation, :service class Implementation def service... end end
If you want to use both Forwardable and SingleForwardable, you can use methods def_instance_delegator and def_single_delegator, etc.
If the object isn't a Module and Class, You can too extend Forwardable module.
printer = String.new printer.extend Forwardable # prepare object for delegation printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts() printer.puts "Howdy!"