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Delegator

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.

Public Class Methods

delegating_block(mid) click to toggle source
 
               # File delegate.rb, line 289
def Delegator.delegating_block(mid)
  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
            
new(obj) click to toggle source

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

 
               # File delegate.rb, line 62
def initialize(obj)
  __setobj__(obj)
end
            

Public Instance Methods

!() click to toggle source
 
               # File delegate.rb, line 133
def !
  !__getobj__
end
            
!=(obj) click to toggle source

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

 
               # File delegate.rb, line 128
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end
            
==(obj) click to toggle source

Returns true if two objects are considered of equal value.

 
               # File delegate.rb, line 120
def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end
            
__getobj__() click to toggle source

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

 
               # File delegate.rb, line 141
def __getobj__
  raise NotImplementedError, "need to define `__getobj__'"
end
            
__setobj__(obj) click to toggle source

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

 
               # File delegate.rb, line 149
def __setobj__(obj)
  raise NotImplementedError, "need to define `__setobj__'"
end
            
freeze click to toggle source

Freeze both the object returned by _getobj_ and self.

 
               # File delegate.rb, line 211
  
            
marshal_dump() click to toggle source

Serialization support for the object returned by _getobj_.

 
               # File delegate.rb, line 156
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) click to toggle source

Reinitializes delegation from a serialized object.

 
               # File delegate.rb, line 168
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_missing(m, *args, &block) click to toggle source

Handles the magic of delegation through _getobj_.

 
               # File delegate.rb, line 69
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
            
methods() click to toggle source

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

 
               # File delegate.rb, line 95
def methods
  __getobj__.methods | super
end
            
protected_methods(all=true) click to toggle source

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

 
               # File delegate.rb, line 111
def protected_methods(all=true)
  __getobj__.protected_methods(all) | super
end
            
public_methods(all=true) click to toggle source

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

 
               # File delegate.rb, line 103
def public_methods(all=true)
  __getobj__.public_methods(all) | super
end
            
respond_to_missing?(m, include_private) click to toggle source

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

 
               # File delegate.rb, line 82
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
            
taint click to toggle source

Taint both the object returned by _getobj_ and self.

 
               # File delegate.rb, line 201
  
            
trust click to toggle source

Trust both the object returned by _getobj_ and self.

 
               # File delegate.rb, line 191
  
            
untaint click to toggle source

Untaint both the object returned by _getobj_ and self.

 
               # File delegate.rb, line 206
  
            
untrust click to toggle source

Untrust both the object returned by _getobj_ and self.

 
               # File delegate.rb, line 196
  
            

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