Disclaimer: Yes, this is performance testing and Ruby. Obviously we choose Ruby for it's other greater qualities. Playing around with performance regarding the various ways you can implement Decorators in Ruby.

decorator_perf.rb

require 'benchmark'
require 'delegate'
require 'forwardable'

class Person
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
end

class PersonDelegator < SimpleDelegator
  def initialize(person)
    super(person)
  end
end

class PersonForwarder
  extend Forwardable

  def_delegator :@person, :name

  def initialize(person)
    @person = person
  end
end

class PersonMissing
  def method_missing(method_name)
    if @person.respond_to?(method_name)
      @person.send(method_name)
    else
      super
    end
  end

  def initialize(person)
    @person = person
  end
end

bob = Person.new('Bob')
decorated_bob = PersonDelegator.new(bob)
forwarded_bob = PersonForwarder.new(bob)
missing_bob = PersonMissing.new(bob)

Benchmark.bmbm do |bm|
  bm.report('Sending message directly') do
    1_000_000.times do
      bob.name
    end
  end

  bm.report 'Sending message through SimpleDelegator' do
    1_000_000.times do
      decorated_bob.name
    end
  end

  bm.report 'Forwarding message using Forwardable' do
    1_000_000.times do
      forwarded_bob.name
    end
  end

  bm.report 'Sending message using method_missing' do
    1_000_000.times do
      missing_bob.name
    end
  end
end

# Sending message directly                  0.090000   0.000000   0.090000 (  0.086165)
# Sending message through SimpleDelegator   0.410000   0.000000   0.410000 (  0.410749)
# Forwarding message using Forwardable      0.230000   0.000000   0.230000 (  0.233133)
# Sending message using method_missing      0.260000   0.000000   0.260000 (  0.254218)
# ------------------------------------------------------------------ total: 0.990000sec

                                              user     system      total        real
# Sending message directly                  0.080000   0.000000   0.080000 (  0.080132)
# Sending message through SimpleDelegator   0.400000   0.000000   0.400000 (  0.403982)
# Forwarding message using Forwardable      0.230000   0.000000   0.230000 (  0.228633)
# Sending message using method_missing      0.250000   0.000000   0.250000 (  0.251649)

Very interesting results !!
I added another case: subclassing the class (and is almost as fast as the original one).

Rehearsal ---------------------------------------------------------------------------
Sending message directly                  0.050000   0.000000   0.050000 (  0.055301)
Sending message through SimpleDelegator   0.280000   0.000000   0.280000 (  0.280395)
Forwarding message using Forwardable      0.150000   0.000000   0.150000 (  0.150432)
Sending message using method_missing      0.160000   0.000000   0.160000 (  0.157218)
Sending message using subclassing         0.050000   0.000000   0.050000 (  0.052206)
------------------------------------------------------------------ total: 0.690000sec

                                              user     system      total        real
Sending message directly                  0.050000   0.000000   0.050000 (  0.050754)
Sending message through SimpleDelegator   0.280000   0.000000   0.280000 (  0.279871)
Forwarding message using Forwardable      0.160000   0.000000   0.160000 (  0.152889)
Sending message using method_missing      0.150000   0.000000   0.150000 (  0.152737)
Sending message using subclassing         0.050000   0.000000   0.050000 (  0.051002)