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Class: Delegator

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Subclasses:
SimpleDelegator
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 of the use of Delegator:

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 Method Summary

Instance Method Summary

  • #!

    Delegates ! to the _getobj_.

  • #!=(obj)

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

  • #==(obj)

    Returns true if two objects are considered of equal value.

  • #__getobj__

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

  • #__setobj__(obj)

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

  • #freeze

    Freeze both the object returned by _getobj_ and self.

  • #marshal_dump

    Serialization support for the object returned by _getobj_.

  • #marshal_load(data)

    Reinitializes delegation from a serialized object.

  • #method_missing(m, *args, &block)

    Handles the magic of delegation through _getobj_.

  • #methods(all = true)

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

  • #protected_methods(all = true)

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

  • #public_methods(all = true)

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

  • #raise

    Use __raise__ if your Delegator does not have a object to delegate the raise method call.

  • #respond_to_missing?(m, include_private) ⇒ Boolean

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

  • #taint

    Taint both the object returned by _getobj_ and self.

  • #trust

    Trust both the object returned by _getobj_ and self.

  • #untaint

    Untaint both the object returned by _getobj_ and self.

  • #untrust

    Untrust both the object returned by _getobj_ and self.

Constructor Details

.new(obj) ⇒ Delegator

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

[ GitHub ] 

  


# File 'lib/delegate.rb', line 71



def initialize(obj)
  __setobj__(obj)
end


  







Dynamic Method Handling

  

    This class handles dynamic methods through the method_missing method




  

    #method_missing(m, *args, &block)  
  



  

    

Handles the magic of delegation through _getobj_.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 78



def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}

  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
end


  







Instance Method Details



  

    #!  
  



  

    

Delegates ! to the _getobj_


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 151



def !
  !__getobj__
end


  








  

    #!=(obj)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 143



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


  








  

    #==(obj)  
  



  

    

Returns true if two objects are considered of equal value.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 135



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


  








  

    #__getobj__  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 159



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


  








  

    #__setobj__(obj)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 167



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


  








  

    #freeze  
  



  

    

Freeze both the object returned by _getobj_ and self.


  



  [ GitHub ]


  

  


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



rdoc_method :method: freeze


  








  

    #marshal_dump  
  



  

    

Serialization support for the object returned by _getobj_.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 174



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)  
  



  

    

Reinitializes delegation from a serialized object.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 186



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


  








  

    #methods(all = true)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 110



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


  








  

    #protected_methods(all = true)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 126



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


  








  

    #public_methods(all = true)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 118



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


  








  

    #raise  
  



  

    

Use __raise__ if your Delegator does not have a object to delegate the raise method call.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 62



rdoc_method :method: raise


  








  

    #respond_to_missing?(m, include_private)  ⇒ Boolean 
  



  

    

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


  





  


  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 95



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


  








  

    #taint  
  



  

    

Taint both the object returned by _getobj_ and self.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 215



rdoc_method :method: taint


  








  

    #trust  
  



  

    

Trust both the object returned by _getobj_ and self.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 205



rdoc_method :method: trust


  








  

    #untaint  
  



  

    

Untaint both the object returned by _getobj_ and self.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 220



rdoc_method :method: untaint


  








  

    #untrust  
  



  

    

Untrust both the object returned by _getobj_ and self.


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 210



rdoc_method :method: untrust