# = 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 if the use of # Delegator: # # class SimpleDelegator < Delegator # def initialize(obj) # super # pass obj to Delegator constructor, required # @delegate_sd_obj = obj # store obj for future use # end # # 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 kernel = ::Kernel.dup kernel.class_eval do [:to_s,:inspect,:=~,:!~,:===,:<=>,:eql?,:hash].each do |m| undef_method m end end include kernel # :stopdoc: def self.const_missing(n) ::Object.const_get(n) end # :startdoc: # # 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\_\_. # def method_missing(m, *args, &block) target = self.__getobj__ begin target.respond_to?(m) ? target.__send__(m, *args, &block) : super(m, *args, &block) ensure $@.delete_if {|t| %r"\A#{Regexp.quote(__FILE__)}:#{__LINE__-2}:"o =~ t} if $@ 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 = self.__getobj__.respond_to?(m, include_private) if r && include_private && !self.__getobj__.respond_to?(m, false) warn "#{caller(3)[0]}: delegator does not forward private method \##{m}" return false end r 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 # # 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) # :nodoc: self.__setobj__(obj.__getobj__.clone) end def initialize_dup(obj) # :nodoc: self.__setobj__(obj.__getobj__.dup) end private :initialize_clone, :initialize_dup ## # :method: trust # Trust both the object returned by \_\_getobj\_\_ and self. # ## # :method: untrust # Untrust both the object returned by \_\_getobj\_\_ and self. # ## # :method: taint # Taint both the object returned by \_\_getobj\_\_ and self. # ## # :method: untaint # Untaint both the object returned by \_\_getobj\_\_ and self. # ## # :method: freeze # Freeze both the object returned by \_\_getobj\_\_ and self. # [:trust, :untrust, :taint, :untaint, :freeze].each do |method| define_method method do __getobj__.send(method) super() end 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__. # # 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__ @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__ begin target.__send__(mid, *args, &block) ensure $@.delete_if {|t| /\A#{Regexp.quote(__FILE__)}:#{__LINE__-2}:/o =~ t} if $@ end end 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 # # 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) klass = Class.new(Delegator) methods = superclass.instance_methods methods -= ::Delegator.public_api methods -= [:to_s,:inspect,:=~,:!~,:===] klass.module_eval do def __getobj__ # :nodoc: @delegate_dc_obj end def __setobj__(obj) # :nodoc: raise ArgumentError, "cannot delegate to self" if self.equal?(obj) @delegate_dc_obj = obj end methods.each do |method| define_method(method, Delegator.delegating_block(method)) end end klass.define_singleton_method :public_instance_methods do |all=true| super(all) - superclass.protected_instance_methods end klass.define_singleton_method :protected_instance_methods do |all=true| super(all) | superclass.protected_instance_methods end return klass end # :enddoc: if __FILE__ == $0 class ExtArray<DelegateClass(Array) def initialize() super([]) end end ary = ExtArray.new p ary.class ary.push 25 p ary ary.push 42 ary.each {|x| p x} foo = Object.new def foo.test 25 end def foo.iter yield self end def foo.error raise 'this is OK' end foo2 = SimpleDelegator.new(foo) p foo2 foo2.instance_eval{print "foo\n"} p foo.test == foo2.test # => true p foo2.iter{[55,true]} # => true foo2.error # raise error! end

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