decorator.rb

class Foo
  def bar
    rand(10).to_s
  end
end

# My interface is the same as Foo because I just decorate that behaviour
class FooDecorator
  attr_accessor :other
  private :other=, :other

  def initialize other
    self.other = other
  end

  def bar
    "The number is #{other.bar}"
  end
end

presenter.rb

class Foo
  def bar
    rand(10).to_s
  end
end

class Baz
  def baz
    rand(100).to_s
  end
end

# My interface is different to Foo or Baz, it provides convenient and consistent access to possibly several underlying objects
class FooBazPresenter
  attr_accessor :foo, :baz
  private :foo=, :foo, :baz=, :baz

  def initialize foo, baz
    self.foo = foo
    self.baz = baz
  end

  def to_s
    "Foo #{foo.bar}, Baz #{baz.bar}"
  end
end