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Class: SimpleDelegator

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::Delegator
Instance Chain:
self, ::Delegator
Inherits: Delegator
Defined in: lib/delegate.rb

Overview

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 User
  def born_on
    Date.new(1989, 9, 10)
  end
end

class UserDecorator < SimpleDelegator
  def birth_year
    born_on.year
  end
end

decorated_user = UserDecorator.new(User.new)
decorated_user.birth_year  #=> 1989
decorated_user.__getobj__  #=> #<User: ...>

A SimpleDelegator instance can take advantage of the fact that SimpleDelegator is a subclass of ::Delegator to call super to have methods called on the object being delegated to.

class SuperArray < SimpleDelegator
  def [](*args)
    super + 1
  end
end

SuperArray.new([1])[0]  #=> 2

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])

Prints:

Elements:  4
 Non-Nil:  4
  Unique:  4

Elements:  8
 Non-Nil:  7
  Unique:  6

Constant Summary

::Delegator - Inherited

KERNEL_RESPOND_TO, VERSION

Class Method Summary

::Delegator - Inherited

.new

Pass in the obj to delegate method calls to.
.const_missing, .delegating_block, .public_api

Instance Method Summary

::Delegator - Inherited

#!

Delegates ! to the _getobj_.
#!=

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

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__

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

Returns true if two objects are considered of equal value.
#freeze,
#marshal_dump

Serialization support for the object returned by _getobj_.
#marshal_load

Reinitializes delegation from a serialized object.
#methods

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

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

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?

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

Handle BasicObject instances.
#initialize_clone, #initialize_dup

Constructor Details

This class inherits a constructor from Delegator

Instance Method Details

#__getobj__

Returns the current object method calls are being delegated to.

[ GitHub ] 

  


# File 'lib/delegate.rb', line 312



def __getobj__
  unless defined?(@delegate_sd_obj)
    return yield if block_given?
    __raise__ ::ArgumentError, "not delegated"
  end
  @delegate_sd_obj
end


  








  

    #__setobj__(obj)  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'lib/delegate.rb', line 334



def __setobj__(obj)
  __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj)
  @delegate_sd_obj = obj
end