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(Delegator.delegating_block): don't hide backtrace from __getobj__ and reduced exception messages when $DEBUG. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@26592 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
337 lines
8.5 KiB
Ruby
337 lines
8.5 KiB
Ruby
# = delegate -- Support for the Delegation Pattern
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#
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# Documentation by James Edward Gray II and Gavin Sinclair
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#
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# == Introduction
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#
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# This library provides three different ways to delegate method calls to an
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# object. The easiest to use is SimpleDelegator. Pass an object to the
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# constructor and all methods supported by the object will be delegated. This
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# object can be changed later.
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#
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# Going a step further, the top level DelegateClass method allows you to easily
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# setup delegation through class inheritance. This is considerably more
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# flexible and thus probably the most common use for this library.
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#
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# Finally, if you need full control over the delegation scheme, you can inherit
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# from the abstract class Delegator and customize as needed. (If you find
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# yourself needing this control, have a look at _forwardable_, also in the
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# standard library. It may suit your needs better.)
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#
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# == Notes
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#
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# Be advised, RDoc will not detect delegated methods.
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#
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# <b>delegate.rb provides full-class delegation via the
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# DelegateClass() method. For single-method delegation via
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# def_delegator(), see forwardable.rb.</b>
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#
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# == Examples
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#
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# === SimpleDelegator
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#
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# Here's a simple example that takes advantage of the fact that
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# SimpleDelegator's delegation object can be changed at any time.
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#
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# class Stats
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# def initialize
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# @source = SimpleDelegator.new([])
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# end
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#
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# def stats( records )
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# @source.__setobj__(records)
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#
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# "Elements: #{@source.size}\n" +
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# " Non-Nil: #{@source.compact.size}\n" +
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# " Unique: #{@source.uniq.size}\n"
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# end
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# end
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#
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# s = Stats.new
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# puts s.stats(%w{James Edward Gray II})
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# puts
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# puts s.stats([1, 2, 3, nil, 4, 5, 1, 2])
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#
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# <i>Prints:</i>
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#
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# Elements: 4
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# Non-Nil: 4
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# Unique: 4
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#
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# Elements: 8
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# Non-Nil: 7
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# Unique: 6
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#
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# === DelegateClass()
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#
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# Here's a sample of use from <i>tempfile.rb</i>.
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#
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# A _Tempfile_ object is really just a _File_ object with a few special rules
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# about storage location and/or when the File should be deleted. That makes for
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# an almost textbook perfect example of how to use delegation.
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#
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# class Tempfile < DelegateClass(File)
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# # constant and class member data initialization...
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#
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# def initialize(basename, tmpdir=Dir::tmpdir)
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# # build up file path/name in var tmpname...
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#
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# @tmpfile = File.open(tmpname, File::RDWR|File::CREAT|File::EXCL, 0600)
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#
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# # ...
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#
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# super(@tmpfile)
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#
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# # below this point, all methods of File are supported...
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# end
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#
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# # ...
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# end
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#
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# === Delegator
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#
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# SimpleDelegator's implementation serves as a nice example here.
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#
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# class SimpleDelegator < Delegator
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# def initialize(obj)
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# super # pass obj to Delegator constructor, required
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# @delegate_sd_obj = obj # store obj for future use
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# end
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#
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# def __getobj__
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# @delegate_sd_obj # return object we are delegating to, required
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# end
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#
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# def __setobj__(obj)
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# @delegate_sd_obj = obj # change delegation object, a feature we're providing
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# end
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#
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# # ...
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# end
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#
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# Delegator is an abstract class used to build delegator pattern objects from
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# subclasses. Subclasses should redefine \_\_getobj\_\_. For a concrete
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# implementation, see SimpleDelegator.
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#
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class Delegator < BasicObject
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kernel = ::Kernel.dup
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kernel.class_eval do
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[:to_s,:inspect,:=~,:!~,:===,:<=>].each do |m|
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undef_method m
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end
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end
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include kernel
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# :stopdoc:
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def self.const_missing(n)
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::Object.const_get(n)
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end
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# :startdoc:
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#
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# Pass in the _obj_ to delegate method calls to. All methods supported by
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# _obj_ will be delegated to.
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#
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def initialize(obj)
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__setobj__(obj)
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end
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# Handles the magic of delegation through \_\_getobj\_\_.
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def method_missing(m, *args, &block)
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target = self.__getobj__
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begin
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target.respond_to?(m) ? target.__send__(m, *args, &block) : super(m, *args, &block)
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ensure
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$@.delete_if {|t| %r"\A#{Regexp.quote(__FILE__)}:#{__LINE__-2}:"o =~ t} if $@
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end
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end
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#
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# Checks for a method provided by this the delegate object by forwarding the
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# call through \_\_getobj\_\_.
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#
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def respond_to_missing?(m, include_private)
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r = self.__getobj__.respond_to?(m, include_private)
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if r && include_private && !self.__getobj__.respond_to?(m, false)
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warn "#{caller(3)[0]}: delegator does not forward private method \##{m}"
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return false
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end
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r
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end
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#
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# Returns true if two objects are considered same.
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#
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def ==(obj)
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return true if obj.equal?(self)
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self.__getobj__ == obj
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end
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#
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# This method must be overridden by subclasses and should return the object
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# method calls are being delegated to.
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#
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def __getobj__
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raise NotImplementedError, "need to define `__getobj__'"
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end
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#
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# This method must be overridden by subclasses and change the object delegate
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# to _obj_.
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#
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def __setobj__(obj)
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raise NotImplementedError, "need to define `__setobj__'"
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end
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# Serialization support for the object returned by \_\_getobj\_\_.
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def marshal_dump
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ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
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[
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:__v2__,
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ivars, ivars.map{|var| instance_variable_get(var)},
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__getobj__
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]
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end
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# Reinitializes delegation from a serialized object.
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def marshal_load(data)
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version, vars, values, obj = data
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if version == :__v2__
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vars.each_with_index{|var, i| instance_variable_set(var, values[i])}
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__setobj__(obj)
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else
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__setobj__(data)
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end
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end
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# :nodoc:
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def dup
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self.class.new(__getobj__.dup)
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end
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# :nodoc:
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def clone
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self.class.new(__getobj__.clone)
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end
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# Freeze self and target at once.
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def freeze
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__getobj__.freeze
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super
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end
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@delegator_api = self.public_instance_methods
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def self.public_api # :nodoc:
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@delegator_api
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end
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end
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#
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# A concrete implementation of Delegator, this class provides the means to
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# delegate all supported method calls to the object passed into the constructor
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# and even to change the object being delegated to at a later time with
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# \_\_setobj\_\_ .
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#
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class SimpleDelegator<Delegator
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# Returns the current object method calls are being delegated to.
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def __getobj__
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@delegate_sd_obj
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end
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#
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# Changes the delegate object to _obj_.
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#
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# It's important to note that this does *not* cause SimpleDelegator's methods
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# to change. Because of this, you probably only want to change delegation
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# to objects of the same type as the original delegate.
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#
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# Here's an example of changing the delegation object.
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#
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# names = SimpleDelegator.new(%w{James Edward Gray II})
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# puts names[1] # => Edward
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# names.__setobj__(%w{Gavin Sinclair})
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# puts names[1] # => Sinclair
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#
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def __setobj__(obj)
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raise ArgumentError, "cannot delegate to self" if self.equal?(obj)
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@delegate_sd_obj = obj
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end
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end
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# :stopdoc:
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def Delegator.delegating_block(mid)
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lambda do |*args, &block|
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target = self.__getobj__
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begin
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target.__send__(mid, *args, &block)
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ensure
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$@.delete_if {|t| /\A#{Regexp.quote(__FILE__)}:#{__LINE__-2}:/o =~ t} if $@
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end
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end
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end
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# :startdoc:
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#
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# The primary interface to this library. Use to setup delegation when defining
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# your class.
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#
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# class MyClass < DelegateClass( ClassToDelegateTo ) # Step 1
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# def initialize
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# super(obj_of_ClassToDelegateTo) # Step 2
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# end
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# end
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#
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def DelegateClass(superclass)
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klass = Class.new(Delegator)
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methods = superclass.public_instance_methods(true)
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methods -= ::Delegator.public_api
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methods -= [:to_s,:inspect,:=~,:!~,:===]
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klass.module_eval {
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def __getobj__ # :nodoc:
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@delegate_dc_obj
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end
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def __setobj__(obj) # :nodoc:
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raise ArgumentError, "cannot delegate to self" if self.equal?(obj)
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@delegate_dc_obj = obj
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end
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}
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klass.module_eval do
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methods.each do |method|
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define_method(method, Delegator.delegating_block(method))
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end
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end
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return klass
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end
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# :enddoc:
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if __FILE__ == $0
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class ExtArray<DelegateClass(Array)
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def initialize()
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super([])
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end
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end
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ary = ExtArray.new
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p ary.class
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ary.push 25
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p ary
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ary.push 42
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ary.each {|x| p x}
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foo = Object.new
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def foo.test
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25
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end
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def foo.iter
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yield self
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end
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def foo.error
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raise 'this is OK'
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end
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foo2 = SimpleDelegator.new(foo)
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p foo2
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foo2.instance_eval{print "foo\n"}
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p foo.test == foo2.test # => true
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p foo2.iter{[55,true]} # => true
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foo2.error # raise error!
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end
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