Class: Delegator

Inherits:
BasicObject
Defined in:
lib/delegate.rb

Overview

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.

Direct Known Subclasses

SimpleDelegator

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(obj) ⇒ Delegator

Pass in the obj to delegate method calls to. All methods supported by obj will be delegated to.



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# File 'lib/delegate.rb', line 69

def initialize(obj)
  __setobj__(obj)
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(m, *args, &block) ⇒ Object

Handles the magic of delegation through _getobj_.



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# File 'lib/delegate.rb', line 76

def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}
  begin
    if r && target.respond_to?(m)
      target.__send__(m, *args, &block)
    elsif ::Kernel.respond_to?(m, true)
      ::Kernel.instance_method(m).bind(self).(*args, &block)
    else
      super(m, *args, &block)
    end
  ensure
    $@.delete_if {|t| %r"\A#{Regexp.quote(__FILE__)}:(?:#{[__LINE__-7, __LINE__-5, __LINE__-3].join('|')}):"o =~ t} if $@
  end
end

Class Method Details

.const_missing(n) ⇒ Object

:stopdoc:



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# File 'lib/delegate.rb', line 60

def self.const_missing(n)
  ::Object.const_get(n)
end

.delegating_block(mid) ⇒ Object

:nodoc:



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# File 'lib/delegate.rb', line 339

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

.public_api ⇒ Object

:nodoc:



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# File 'lib/delegate.rb', line 238

def self.public_api   # :nodoc:
  @delegator_api
end

Instance Method Details

#! ⇒ Object

Delegates ! to the _getobj_



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# File 'lib/delegate.rb', line 152

def !
  !__getobj__
end

#!=(obj) ⇒ Object

Returns true if two objects are not considered of equal value.



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# File 'lib/delegate.rb', line 144

def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

#==(obj) ⇒ Object

Returns true if two objects are considered of equal value.



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# File 'lib/delegate.rb', line 136

def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

#__getobj__ ⇒ Object

This method must be overridden by subclasses and should return the object method calls are being delegated to.



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# File 'lib/delegate.rb', line 160

def __getobj__
  __raise__ ::NotImplementedError, "need to define `__getobj__'"
end

#__setobj__(obj) ⇒ Object

This method must be overridden by subclasses and change the object delegate to obj.



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# File 'lib/delegate.rb', line 168

def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end

#marshal_dump ⇒ Object

Serialization support for the object returned by _getobj_.



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# File 'lib/delegate.rb', line 175

def marshal_dump
  ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
  [
    :__v2__,
    ivars, ivars.map{|var| instance_variable_get(var)},
    __getobj__
  ]
end

#marshal_load(data) ⇒ Object

Reinitializes delegation from a serialized object.



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# File 'lib/delegate.rb', line 187

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

#method ⇒ Object

:method: freeze Freeze both the object returned by _getobj_ and self.



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# File 'lib/delegate.rb', line 230

[:trust, :untrust, :taint, :untaint, :freeze].each do |method|
  define_method method do
    __getobj__.send(method)
    super()
  end
end

#methods(all = true) ⇒ Object

Returns the methods available to this delegate object as the union of this object’s and _getobj_ methods.



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# File 'lib/delegate.rb', line 111

def methods(all=true)
  __getobj__.methods(all) | super
end

#protected_methods(all = true) ⇒ Object

Returns the methods available to this delegate object as the union of this object’s and _getobj_ protected methods.



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# File 'lib/delegate.rb', line 127

def protected_methods(all=true)
  __getobj__.protected_methods(all) | super
end

#public_methods(all = true) ⇒ Object

Returns the methods available to this delegate object as the union of this object’s and _getobj_ public methods.



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# File 'lib/delegate.rb', line 119

def public_methods(all=true)
  __getobj__.public_methods(all) | super
end

#respond_to_missing?(m, include_private) ⇒ Boolean

Checks for a method provided by this the delegate object by forwarding the call through _getobj_.

Returns:

  • (Boolean) 


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# File 'lib/delegate.rb', line 96

def respond_to_missing?(m, include_private)
  r = true
  target = self.__getobj__ {r = false}
  r &&= target.respond_to?(m, include_private)
  if r && include_private && !target.respond_to?(m, false)
    warn "#{caller(3)[0]}: delegator does not forward private method \##{m}"
    return false
  end
  r
end