forwardable - Support for the Delegation Pattern
$Release Version: 1.1$ $Revision: 11708 $ $Date: 2007-02-12 16:01:19 -0700 (Mon, 12 Feb 2007) $ by Keiju ISHITSUKA(firstname.lastname@example.org) 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. You can use Forwardable to setup this delegation at the class level, or SingleForwardable to handle it at the object level.
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 def initialize @q = [ ] # prepare delegate object end # setup prefered 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
printer = String.new printer.extend # prepare object for delegation printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts() printer.puts "Howdy!"