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  • delegate.rb

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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, 09, 10)

class UserDecorator < SimpleDelegator
  def birth_year

decorated_user =
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[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 =[])

  def stats(records)

    "Elements:  #{@source.size}\n" +
    " Non-Nil:  #{@source.compact.size}\n" +
    "  Unique:  #{@source.uniq.size}\n"

s =
puts s.stats(%w{James Edward Gray II})
puts s.stats([1, 2, 3, nil, 4, 5, 1, 2])


Elements:  4
 Non-Nil:  4
  Unique:  4

Elements:  8
 Non-Nil:  7
  Unique:  6

Public Instance Methods

__getobj__() click to toggle source

Returns the current object method calls are being delegated to.

               # File delegate.rb, line 311
def __getobj__
  unless defined?(@delegate_sd_obj)
    return yield if block_given?
    __raise__ ::ArgumentError, "not delegated"
__setobj__(obj) click to toggle source

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 ={James Edward Gray II})
puts names[1]    # => Edward
names.__setobj__(%w{Gavin Sinclair})
puts names[1]    # => Sinclair
               # File delegate.rb, line 333
def __setobj__(obj)
  __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj)
  @delegate_sd_obj = obj

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