How to use alias_method_chain

alias_method_chain.rb

require 'active_support/core_ext/module/aliasing'

class A
  def foo
    'foo'
  end
end

class B < A
  def foo_with_bar
    'foobar'
  end
  alias_method_chain :foo, :bar
end

a = A.new
a.foo # => 'foo'

b = B.new
b.foo # => 'foobar'
b.foo_with_bar # => 'foobar'
b.foo_without_bar # => 'foo'