#
# forwardable.rb -
# $Release Version: 1.1$
# $Revision: 38689 $
# 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
# 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)
#
# 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!"
#
# == Another example
#
# 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
#
# This should output:
#
# 2
# 3
# 4
# 5
# 6
# Ruby
# nil
#
# == 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+.
#
module Forwardable
# Version of +forwardable.rb+
FORWARDABLE_VERSION = "1.1.0"
@debug = nil
class << self
# If true, <tt>__FILE__</tt> will remain in the backtrace in the event an
# Exception is raised.
attr_accessor :debug
end
# 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 instance_delegate(hash)
hash.each{ |methods, accessor|
methods = [methods] 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__")
for method in methods
def_instance_delegator(accessor, method)
end
end
# Define +method+ as delegator instance method with an optional
# alias name +ali+. Method calls to +ali+ will be delegated to
# +accessor.method+.
#
# class MyQueue
# extend Forwardable
# attr_reader :queue
# def initialize
# @queue = []
# end
#
# def_delegator :@queue, :push, :mypush
# end
#
# q = MyQueue.new
# q.mypush 42
# q.queue #=> [42]
# q.push 23 #=> NoMethodError
#
def def_instance_delegator(accessor, method, ali = method)
line_no = __LINE__; str = %{
def #{ali}(*args, &block)
begin
#{accessor}.__send__(:#{method}, *args, &block)
rescue Exception
$@.delete_if{|s| %r"#{Regexp.quote(__FILE__)}"o =~ s} unless Forwardable::debug
::Kernel::raise
end
end
}
# If it's not a class or module, it's an instance
begin
module_eval(str, __FILE__, line_no)
rescue
instance_eval(str, __FILE__, line_no)
end
end
alias delegate instance_delegate
alias def_delegators def_instance_delegators
alias def_delegator def_instance_delegator
end
# 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 used to set up delegation for a Class or Module.
#
# class Implementation
# def self.service
# puts "serviced!"
# end
# end
#
# module Facade
# extend SingleForwardable
# def_delegator :Implementation, :service
# end
#
# Facade.service #=> serviced!
#
# If you want to use both Forwardable and SingleForwardable, you can
# use methods def_instance_delegator and def_single_delegator, etc.
module SingleForwardable
# 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 single_delegate(hash)
hash.each{ |methods, accessor|
methods = [methods] unless methods.respond_to?(:each)
methods.each{ |method|
def_single_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_single_delegators(accessor, *methods)
methods.delete("__send__")
methods.delete("__id__")
for method in methods
def_single_delegator(accessor, method)
end
end
# :call-seq:
# def_single_delegator(accessor, method, new_name=method)
#
# Defines a method _method_ which delegates to _accessor_ (i.e. it calls
# the method of the same name in _accessor_). If _new_name_ is
# provided, it is used as the name for the delegate method.
def def_single_delegator(accessor, method, ali = method)
str = %{
def #{ali}(*args, &block)
begin
#{accessor}.__send__(:#{method}, *args, &block)
rescue Exception
$@.delete_if{|s| %r"#{Regexp.quote(__FILE__)}"o =~ s} unless Forwardable::debug
::Kernel::raise
end
end
}
instance_eval(str, __FILE__, __LINE__)
end
alias delegate single_delegate
alias def_delegators def_single_delegators
alias def_delegator def_single_delegator
end
