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Diffstat (limited to 'trunk/lib/forwardable.rb')
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diff --git a/trunk/lib/forwardable.rb b/trunk/lib/forwardable.rb new file mode 100644 index 0000000000..a4af0217d0 --- /dev/null +++ b/trunk/lib/forwardable.rb @@ -0,0 +1,177 @@ +# +# forwardable.rb - +# $Release Version: 1.1$ +# $Revision$ +# by Keiju ISHITSUKA(keiju@ishitsuka.com) +# original definition by delegator.rb +# Revised by Daniel J. Berger with suggestions from Florian Gross. +# +# 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. +# +# == Notes +# +# Be advised, RDoc will not detect delegated methods. +# +# <b>forwardable.rb provides single-method delegation via the +# def_delegator() and def_delegators() methods. For full-class +# delegation via DelegateClass(), see delegate.rb.</b> +# +# == 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 +# +# <i>Prints:</i> +# +# 2 +# 3 +# 4 +# 5 +# 6 +# Ruby +# nil +# +# Forwardable can be used to setup delegation at the object level as well. +# +# printer = String.new +# printer.extend Forwardable # prepare object for delegation +# printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts() +# printer.puts "Howdy!" +# +# <i>Prints:</i> +# +# Howdy! + +# +# The Forwardable module provides delegation of specified +# methods to a designated object, using the methods #def_delegator +# and #def_delegators. +# +# For example, say you have a class RecordCollection which +# contains an array <tt>@records</tt>. You could provide the lookup method +# #record_number(), which simply calls #[] on the <tt>@records</tt> +# array, like this: +# +# class RecordCollection +# extend Forwardable +# def_delegator :@records, :[], :record_number +# end +# +# Further, if you wish to provide the methods #size, #<<, and #map, +# all of which delegate to @records, this is how you can do it: +# +# class RecordCollection +# # extend Forwardable, but we did that above +# def_delegators :@records, :size, :<<, :map +# end +# f = Foo.new +# f.printf ... +# f.gets +# f.content_at(1) +# +# Also see the example at forwardable.rb. + +module Forwardable + FORWARDABLE_VERSION = "1.0.0" + + # Takes a hash as its argument. The key is a symbol or an array of + # symbols. These symbols correspond to method names. The value is + # the accessor to which the methods will be delegated. + # + # :call-seq: + # delegate method => accessor + # delegate [method, method, ...] => accessor + # + def delegate(hash) + hash.each{ |methods, accessor| + methods = methods.to_s unless methods.respond_to?(:each) + methods.each{ |method| + def_instance_delegator(accessor, method) + } + } + end + + # + # Shortcut for defining multiple delegator methods, but with no + # provision for using a different name. The following two code + # samples have the same effect: + # + # def_delegators :@records, :size, :<<, :map + # + # def_delegator :@records, :size + # def_delegator :@records, :<< + # def_delegator :@records, :map + # + def def_instance_delegators(accessor, *methods) + methods.delete("__send__") + methods.delete("__id__") + methods.each{ |method| + def_instance_delegator(accessor, method) + } + end + + # + # Defines a method _method_ which delegates to _obj_ (i.e. it calls + # the method of the same name in _obj_). If _new_name_ is + # provided, it is used as the name for the delegate method. + # + def def_instance_delegator(accessor, method, ali = method) + str = %Q{ + def #{ali}(*args, &block) + #{accessor}.send(:#{method}, *args, &block) + end + } + + # If it's not a class or module, it's an instance + begin + module_eval(str) + rescue + instance_eval(str) + end + end + + alias def_delegators def_instance_delegators + alias def_delegator def_instance_delegator +end + +# compatibility +SingleForwardable = Forwardable |