forwardable - Support for the Delegation Pattern
$Release Version: 1.1$
$Revision: 16857 $
$Date: 2008-06-06 17:05:24 +0900 (Fri, 06 Jun 2008) $
by Keiju ISHITSUKA([email protected])
Documentation by James Edward Gray II and Gavin Sinclair
Introduction
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.
Notes
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.
Examples
Forwardable
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
Prints:
2
3
4
5
6
Ruby
nil
SingleForwardable
printer = String.new
printer.extend SingleForwardable # prepare object for delegation
printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts()
printer.puts "Howdy!"
Prints:
Howdy!