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Diffstat (limited to 'lib/delegate.rb')
| -rw-r--r-- | lib/delegate.rb | 459 |
1 files changed, 459 insertions, 0 deletions
diff --git a/lib/delegate.rb b/lib/delegate.rb new file mode 100644 index 0000000000..0cc3ddb1b0 --- /dev/null +++ b/lib/delegate.rb @@ -0,0 +1,459 @@ +# frozen_string_literal: true +# = delegate -- Support for the Delegation Pattern +# +# Documentation by James Edward Gray II and Gavin Sinclair + +## +# This library provides three different ways to delegate method calls to an +# object. The easiest to use is SimpleDelegator. Pass an object to the +# constructor and all methods supported by the object will be delegated. This +# object can be changed later. +# +# Going a step further, the top level DelegateClass method allows you to easily +# setup delegation through class inheritance. This is considerably more +# flexible and thus probably the most common use for this library. +# +# Finally, if you need full control over the delegation scheme, you can inherit +# from the abstract class Delegator and customize as needed. (If you find +# yourself needing this control, have a look at Forwardable which is also in +# the standard library. It may suit your needs better.) +# +# SimpleDelegator's implementation serves as a nice example of the use of +# Delegator: +# +# require 'delegate' +# +# class SimpleDelegator < Delegator +# def __getobj__ +# @delegate_sd_obj # return object we are delegating to, required +# end +# +# def __setobj__(obj) +# @delegate_sd_obj = obj # change delegation object, +# # a feature we're providing +# end +# end +# +# == Notes +# +# Be advised, RDoc will not detect delegated methods. +# +class Delegator < BasicObject + # The version string + VERSION = "0.6.1" + + kernel = ::Kernel.dup + kernel.class_eval do + alias __raise__ raise + [:to_s, :inspect, :!~, :===, :<=>, :hash].each do |m| + undef_method m + end + private_instance_methods.each do |m| + if /\Ablock_given\?\z|\Aiterator\?\z|\A__.*__\z/ =~ m + next + end + undef_method m + end + end + include kernel + + # :stopdoc: + def self.const_missing(n) + ::Object.const_get(n) + end + # :startdoc: + + ## + # :method: raise + # Use #__raise__ if your Delegator does not have a object to delegate the + # #raise method call. + # + + # + # Pass in the _obj_ to delegate method calls to. All methods supported by + # _obj_ will be delegated to. + # + def initialize(obj) + __setobj__(obj) + end + + # + # Handles the magic of delegation through +__getobj__+. + # + ruby2_keywords def method_missing(m, *args, &block) + r = true + target = self.__getobj__ {r = false} + + if r && target_respond_to?(target, m, false) + target.__send__(m, *args, &block) + elsif ::Kernel.method_defined?(m) || ::Kernel.private_method_defined?(m) + ::Kernel.instance_method(m).bind_call(self, *args, &block) + else + super(m, *args, &block) + end + end + + # + # Checks for a method provided by this the delegate object by forwarding the + # call through +__getobj__+. + # + def respond_to_missing?(m, include_private) + r = true + target = self.__getobj__ {r = false} + r &&= target_respond_to?(target, m, include_private) + if r && include_private && !target_respond_to?(target, m, false) + warn "delegator does not forward private method \##{m}", uplevel: 3 + return false + end + r + end + + KERNEL_RESPOND_TO = ::Kernel.instance_method(:respond_to?) # :nodoc: + private_constant :KERNEL_RESPOND_TO + + # Handle BasicObject instances + private def target_respond_to?(target, m, include_private) + case target + when Object + target.respond_to?(m, include_private) + else + if KERNEL_RESPOND_TO.bind_call(target, :respond_to?) + target.respond_to?(m, include_private) + else + KERNEL_RESPOND_TO.bind_call(target, m, include_private) + end + end + end + + # + # Returns the methods available to this delegate object as the union + # of this object's and +__getobj__+ methods. + # + def methods(all=true) + __getobj__.methods(all) | super + end + + # + # Returns the methods available to this delegate object as the union + # of this object's and +__getobj__+ public methods. + # + def public_methods(all=true) + __getobj__.public_methods(all) | super + end + + # + # Returns the methods available to this delegate object as the union + # of this object's and +__getobj__+ protected methods. + # + def protected_methods(all=true) + __getobj__.protected_methods(all) | super + end + + # Note: no need to specialize private_methods, since they are not forwarded + + # + # Returns true if two objects are considered of equal value. + # + def ==(obj) + return true if obj.equal?(self) + self.__getobj__ == obj + end + + # + # Returns true if two objects are not considered of equal value. + # + def !=(obj) + return false if obj.equal?(self) + __getobj__ != obj + end + + # + # Returns true if two objects are considered of equal value. + # + def eql?(obj) + return true if obj.equal?(self) + obj.eql?(__getobj__) + end + + # + # Delegates ! to the +__getobj__+ + # + def ! + !__getobj__ + end + + # + # This method must be overridden by subclasses and should return the object + # method calls are being delegated to. + # + def __getobj__ + __raise__ ::NotImplementedError, "need to define '__getobj__'" + end + + # + # This method must be overridden by subclasses and change the object delegate + # to _obj_. + # + def __setobj__(obj) + __raise__ ::NotImplementedError, "need to define '__setobj__'" + end + + # + # Serialization support for the object returned by +__getobj__+. + # + def marshal_dump + ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var} + [ + :__v2__, + ivars, ivars.map {|var| instance_variable_get(var)}, + __getobj__ + ] + end + + # + # Reinitializes delegation from a serialized object. + # + def marshal_load(data) + version, vars, values, obj = data + if version == :__v2__ + vars.each_with_index {|var, i| instance_variable_set(var, values[i])} + __setobj__(obj) + else + __setobj__(data) + end + end + + def initialize_clone(obj, freeze: nil) # :nodoc: + self.__setobj__(obj.__getobj__.clone(freeze: freeze)) + end + def initialize_dup(obj) # :nodoc: + self.__setobj__(obj.__getobj__.dup) + end + private :initialize_clone, :initialize_dup + + ## + # :method: freeze + # Freeze both the object returned by +__getobj__+ and self. + # + def freeze + __getobj__.freeze + super() + end + + @delegator_api = self.public_instance_methods + def self.public_api # :nodoc: + @delegator_api + end +end + +## +# A concrete implementation of Delegator, this class provides the means to +# delegate all supported method calls to the object passed into the constructor +# and even to change the object being delegated to at a later time with +# #__setobj__. +# +# class User +# def born_on +# Date.new(1989, 9, 10) +# end +# end +# +# require 'delegate' +# +# class UserDecorator < SimpleDelegator +# def birth_year +# born_on.year +# end +# end +# +# decorated_user = UserDecorator.new(User.new) +# decorated_user.birth_year #=> 1989 +# decorated_user.__getobj__ #=> #<User: ...> +# +# A SimpleDelegator instance can take advantage of the fact that SimpleDelegator +# is a subclass of +Delegator+ to call <tt>super</tt> to have methods called on +# the object being delegated to. +# +# class SuperArray < SimpleDelegator +# def [](*args) +# super + 1 +# end +# end +# +# SuperArray.new([1])[0] #=> 2 +# +# Here's a simple example that takes advantage of the fact that +# SimpleDelegator's delegation object can be changed at any time. +# +# class Stats +# def initialize +# @source = SimpleDelegator.new([]) +# end +# +# def stats(records) +# @source.__setobj__(records) +# +# "Elements: #{@source.size}\n" + +# " Non-Nil: #{@source.compact.size}\n" + +# " Unique: #{@source.uniq.size}\n" +# end +# end +# +# s = Stats.new +# puts s.stats(%w{James Edward Gray II}) +# puts +# puts s.stats([1, 2, 3, nil, 4, 5, 1, 2]) +# +# Prints: +# +# Elements: 4 +# Non-Nil: 4 +# Unique: 4 +# +# Elements: 8 +# Non-Nil: 7 +# Unique: 6 +# +class SimpleDelegator < Delegator + # Returns the current object method calls are being delegated to. + def __getobj__ + unless defined?(@delegate_sd_obj) + return yield if block_given? + __raise__ ::ArgumentError, "not delegated" + end + @delegate_sd_obj + end + + # + # Changes the delegate object to _obj_. + # + # It's important to note that this does *not* cause SimpleDelegator's methods + # to change. Because of this, you probably only want to change delegation + # to objects of the same type as the original delegate. + # + # Here's an example of changing the delegation object. + # + # names = SimpleDelegator.new(%w{James Edward Gray II}) + # puts names[1] # => Edward + # names.__setobj__(%w{Gavin Sinclair}) + # puts names[1] # => Sinclair + # + def __setobj__(obj) + __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj) + @delegate_sd_obj = obj + end +end + +def Delegator.delegating_block(mid) # :nodoc: + lambda do |*args, &block| + target = self.__getobj__ + target.__send__(mid, *args, &block) + end.ruby2_keywords +end + +# +# The primary interface to this library. Use to setup delegation when defining +# your class. +# +# class MyClass < DelegateClass(ClassToDelegateTo) # Step 1 +# def initialize +# super(obj_of_ClassToDelegateTo) # Step 2 +# end +# end +# +# or: +# +# MyClass = DelegateClass(ClassToDelegateTo) do # Step 1 +# def initialize +# super(obj_of_ClassToDelegateTo) # Step 2 +# end +# end +# +# Here's a sample of use from Tempfile which is really a File object with a +# few special rules about storage location and when the File should be +# deleted. That makes for an almost textbook perfect example of how to use +# delegation. +# +# class Tempfile < DelegateClass(File) +# # constant and class member data initialization... +# +# def initialize(basename, tmpdir=Dir::tmpdir) +# # build up file path/name in var tmpname... +# +# @tmpfile = File.open(tmpname, File::RDWR|File::CREAT|File::EXCL, 0600) +# +# # ... +# +# super(@tmpfile) +# +# # below this point, all methods of File are supported... +# end +# +# # ... +# end +# +def DelegateClass(superclass, &block) + klass = Class.new(Delegator) + ignores = [*::Delegator.public_api, :to_s, :inspect, :=~, :!~, :===] + protected_instance_methods = superclass.protected_instance_methods + protected_instance_methods -= ignores + public_instance_methods = superclass.public_instance_methods + public_instance_methods -= ignores + + normal, special = public_instance_methods.partition { |m| m.match?(/\A[a-zA-Z]\w*[!\?]?\z/) } + + source = normal.map do |method| + "def #{method}(...); __getobj__.#{method}(...); end" + end + + protected_instance_methods.each do |method| + source << "def #{method}(...); __getobj__.__send__(#{method.inspect}, ...); end" + end + + klass.module_eval do + def __getobj__ # :nodoc: + unless defined?(@delegate_dc_obj) + return yield if block_given? + __raise__ ::ArgumentError, "not delegated" + end + @delegate_dc_obj + end + + def __setobj__(obj) # :nodoc: + __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj) + @delegate_dc_obj = obj + end + + class_eval(source.join(";"), __FILE__, __LINE__) + + special.each do |method| + define_method(method, Delegator.delegating_block(method)) + end + + protected(*protected_instance_methods) + end + + klass.define_singleton_method :public_instance_methods do |all=true| + super(all) | superclass.public_instance_methods + end + klass.define_singleton_method :protected_instance_methods do |all=true| + super(all) | superclass.protected_instance_methods + end + klass.define_singleton_method :instance_methods do |all=true| + super(all) | superclass.instance_methods + end + klass.define_singleton_method :public_instance_method do |name| + super(name) + rescue NameError + raise unless self.public_instance_methods.include?(name) + superclass.public_instance_method(name) + end + klass.define_singleton_method :instance_method do |name| + super(name) + rescue NameError + raise unless self.instance_methods.include?(name) + superclass.instance_method(name) + end + klass.module_eval(&block) if block + return klass +end |