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Diffstat (limited to 'lib/forwardable.rb')
| -rw-r--r-- | lib/forwardable.rb | 314 |
1 files changed, 314 insertions, 0 deletions
diff --git a/lib/forwardable.rb b/lib/forwardable.rb new file mode 100644 index 0000000000..175d6d9c6b --- /dev/null +++ b/lib/forwardable.rb @@ -0,0 +1,314 @@ +# frozen_string_literal: false +# +# 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 + + + +# 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: +# +# require 'forwardable' +# +# class RecordCollection +# attr_accessor :records +# extend Forwardable +# def_delegator :@records, :[], :record_number +# end +# +# We can use the lookup method like so: +# +# r = RecordCollection.new +# r.records = [4,5,6] +# r.record_number(0) # => 4 +# +# 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 # re-open RecordCollection class +# def_delegators :@records, :size, :<<, :map +# end +# +# r = RecordCollection.new +# r.records = [1,2,3] +# r.record_number(0) # => 1 +# r.size # => 3 +# r << 4 # => [1, 2, 3, 4] +# r.map { |x| x * 2 } # => [2, 4, 6, 8] +# +# You can even extend regular objects with Forwardable. +# +# my_hash = Hash.new +# my_hash.extend Forwardable # prepare object for delegation +# my_hash.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts() +# my_hash.puts "Howdy!" +# +# == Another example +# +# You could use Forwardable as an alternative to inheritance, when you don't want +# to inherit all methods from the superclass. For instance, here is how you might +# add a range of +Array+ instance methods to a new class +Queue+: +# +# 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 = Thread::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+ + VERSION = "1.4.0" + VERSION.freeze + + # Version for backward compatibility + FORWARDABLE_VERSION = VERSION + FORWARDABLE_VERSION.freeze + + @debug = nil + class << self + # ignored + 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, instance variable + # names, or constant names (see def_delegator). 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 do |methods, accessor| + unless defined?(methods.each) + def_instance_delegator(accessor, methods) + else + methods.each {|method| def_instance_delegator(accessor, method)} + end + end + 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.each do |method| + next if /\A__(?:send|id)__\z/ =~ method + 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+. +accessor+ should be a method name, instance + # variable name, or constant name. Use the full path to the + # constant if providing the constant name. + # Returns the name of the method defined. + # + # class MyQueue + # CONST = 1 + # extend Forwardable + # attr_reader :queue + # def initialize + # @queue = [] + # end + # + # def_delegator :@queue, :push, :mypush + # def_delegator 'MyQueue::CONST', :to_i + # end + # + # q = MyQueue.new + # q.mypush 42 + # q.queue #=> [42] + # q.push 23 #=> NoMethodError + # q.to_i #=> 1 + # + def def_instance_delegator(accessor, method, ali = method) + gen = Forwardable._delegator_method(self, accessor, method, ali) + + # If it's not a class or module, it's an instance + mod = Module === self ? self : singleton_class + mod.module_eval(&gen) + end + + alias delegate instance_delegate + alias def_delegators def_instance_delegators + alias def_delegator def_instance_delegator + + # :nodoc: + def self._delegator_method(obj, accessor, method, ali) + accessor = accessor.to_s unless Symbol === accessor + + if Module === obj ? + obj.method_defined?(accessor) || obj.private_method_defined?(accessor) : + obj.respond_to?(accessor, true) + accessor = "(#{accessor}())" + end + + args = RUBY_VERSION >= '2.7' ? '...' : '*args, &block' + method_call = ".__send__(:#{method}, #{args})" + if method.match?(/\A[_a-zA-Z]\w*[?!]?\z/) + loc, = caller_locations(2,1) + pre = "_ =" + mesg = "#{Module === obj ? obj : obj.class}\##{ali} at #{loc.path}:#{loc.lineno} forwarding to private method " + method_call = <<~RUBY.chomp + if defined?(_.#{method}) + _.#{method}(#{args}) + else + ::Kernel.warn #{mesg.dump}"\#{_.class}"'##{method}', uplevel: 1 + _#{method_call} + end + RUBY + end + + eval(<<~RUBY, nil, __FILE__, __LINE__ + 1) + proc do + def #{ali}(#{args}) + #{pre}#{accessor} + #{method_call} + end + end + RUBY + end +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 do |methods, accessor| + unless defined?(methods.each) + def_single_delegator(accessor, methods) + else + methods.each {|method| def_single_delegator(accessor, method)} + end + end + 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.each do |method| + next if /\A__(?:send|id)__\z/ =~ method + 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. + # Returns the name of the method defined. + def def_single_delegator(accessor, method, ali = method) + gen = Forwardable._delegator_method(self, accessor, method, ali) + + instance_eval(&gen) + end + + alias delegate single_delegate + alias def_delegators def_single_delegators + alias def_delegator def_single_delegator +end |