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__.

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
Methods
#
Instance Public methods
__getobj__()

Returns the current object method calls are being delegated to.

Source: show | on GitHub 

# File lib/delegate.rb, line 267
def __getobj__
  @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

Source: show | on GitHub 

# File lib/delegate.rb, line 285
def __setobj__(obj)
  raise ArgumentError, "cannot delegate to self" if self.equal?(obj)
  @delegate_sd_obj = obj
end