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- # = delegate -- Support for the Delegation Pattern
- #
- # Documentation by James Edward Gray II and Gavin Sinclair
- #
- # == Introduction
- #
- # 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_, also in the
- # standard library. It may suit your needs better.)
- #
- # == Notes
- #
- # Be advised, RDoc will not detect delegated methods.
- #
- # <b>delegate.rb provides full-class delegation via the
- # DelegateClass() method. For single-method delegation via
- # def_delegator(), see forwardable.rb.</b>
- #
- # == Examples
- #
- # === SimpleDelegator
- #
- # 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])
- #
- # <i>Prints:</i>
- #
- # Elements: 4
- # Non-Nil: 4
- # Unique: 4
- #
- # Elements: 8
- # Non-Nil: 7
- # Unique: 6
- #
- # === DelegateClass()
- #
- # Here's a sample of use from <i>tempfile.rb</i>.
- #
- # A _Tempfile_ object is really just a _File_ object with a few special rules
- # about storage location and/or 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
- #
- # === Delegator
- #
- # SimpleDelegator's implementation serves as a nice example here.
- #
- # class SimpleDelegator < Delegator
- # def initialize(obj)
- # super # pass obj to Delegator constructor, required
- # @_sd_obj = obj # store obj for future use
- # end
- #
- # def __getobj__
- # @_sd_obj # return object we are delegating to, required
- # end
- #
- # def __setobj__(obj)
- # @_sd_obj = obj # change delegation object, a feature we're providing
- # end
- #
- # # ...
- # end
- #
- # Delegator is an abstract class used to build delegator pattern objects from
- # subclasses. Subclasses should redefine \_\_getobj\_\_. For a concrete
- # implementation, see SimpleDelegator.
- #
- class Delegator
- IgnoreBacktracePat = %r"\A#{Regexp.quote(__FILE__)}:\d+:in `"
- #
- # Pass in the _obj_ to delegate method calls to. All methods supported by
- # _obj_ will be delegated to.
- #
- def initialize(obj)
- preserved = ::Kernel.public_instance_methods(false)
- preserved -= ["to_s","to_a","inspect","==","=~","==="]
- for t in self.class.ancestors
- preserved |= t.public_instance_methods(false)
- preserved |= t.private_instance_methods(false)
- preserved |= t.protected_instance_methods(false)
- break if t == Delegator
- end
- preserved << "singleton_method_added"
- for method in obj.methods
- next if preserved.include? method
- begin
- eval <<-EOS, nil, __FILE__, __LINE__+1
- def self.#{method}(*args, &block)
- begin
- __getobj__.__send__(:#{method}, *args, &block)
- ensure
- $@.delete_if{|s|IgnoreBacktracePat=~s} if $@
- end
- end
- EOS
- rescue SyntaxError
- raise NameError, "invalid identifier %s" % method, caller(4)
- end
- end
- end
- alias initialize_methods initialize
- # Handles the magic of delegation through \_\_getobj\_\_.
- def method_missing(m, *args, &block)
- target = self.__getobj__
- unless target.respond_to?(m)
- super(m, *args, &block)
- end
- target.__send__(m, *args, &block)
- end
- #
- # Checks for a method provided by this the delegate object by fowarding the
- # call through \_\_getobj\_\_.
- #
- def respond_to?(m, include_private = false)
- return true if super
- return self.__getobj__.respond_to?(m, include_private)
- 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
- # Serialization support for the object returned by \_\_getobj\_\_.
- def marshal_dump
- __getobj__
- end
- # Reinitializes delegation from a serialized object.
- def marshal_load(obj)
- initialize_methods(obj)
- __setobj__(obj)
- 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 SimpleDelegator<Delegator
- # Pass in the _obj_ you would like to delegate method calls to.
- def initialize(obj)
- super
- @_sd_obj = obj
- end
- # Returns the current object method calls are being delegated to.
- def __getobj__
- @_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)
- @_sd_obj = obj
- end
- # Clone support for the object returned by \_\_getobj\_\_.
- def clone
- new = super
- new.__setobj__(__getobj__.clone)
- new
- end
- # Duplication support for the object returned by \_\_getobj\_\_.
- def dup
- new = super
- new.__setobj__(__getobj__.clone)
- new
- end
- end
- # :stopdoc:
- # backward compatibility ^_^;;;
- Delegater = Delegator
- SimpleDelegater = SimpleDelegator
- # :startdoc:
- #
- # 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
- #
- def DelegateClass(superclass)
- klass = Class.new
- methods = superclass.public_instance_methods(true)
- methods -= ::Kernel.public_instance_methods(false)
- methods |= ["to_s","to_a","inspect","==","=~","==="]
- klass.module_eval {
- def initialize(obj) # :nodoc:
- @_dc_obj = obj
- end
- def method_missing(m, *args, &block) # :nodoc:
- unless @_dc_obj.respond_to?(m)
- super(m, *args, &block)
- end
- @_dc_obj.__send__(m, *args, &block)
- end
- def respond_to?(m, include_private = false) # :nodoc:
- return true if super
- return @_dc_obj.respond_to?(m, include_private)
- end
- def __getobj__ # :nodoc:
- @_dc_obj
- end
- def __setobj__(obj) # :nodoc:
- raise ArgumentError, "cannot delegate to self" if self.equal?(obj)
- @_dc_obj = obj
- end
- def clone # :nodoc:
- new = super
- new.__setobj__(__getobj__.clone)
- new
- end
- def dup # :nodoc:
- new = super
- new.__setobj__(__getobj__.clone)
- new
- end
- }
- for method in methods
- begin
- klass.module_eval <<-EOS, __FILE__, __LINE__+1
- def #{method}(*args, &block)
- begin
- @_dc_obj.__send__(:#{method}, *args, &block)
- ensure
- $@.delete_if{|s| ::Delegator::IgnoreBacktracePat =~ s} if $@
- end
- end
- EOS
- rescue SyntaxError
- raise NameError, "invalid identifier %s" % method, caller(3)
- end
- 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
- foo = Object.new
- def foo.test
- 25
- end
- def foo.error
- raise 'this is OK'
- end
- foo2 = SimpleDelegator.new(foo)
- p foo.test == foo2.test # => true
- foo2.error # raise error!
- end
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