gistfile1.rb

class A
  def foo
    puts 'original'
  end
  
  alias bar foo
  
  def foo
    puts 'modified'
  end
end

A.new.bar # => "original"

# -------------------------------------

class A
  def foo
    puts 'original'
  end
end

class B < A
  alias bar foo
end

class A
  def foo
    puts 'modified'
  end
end

B.new.bar # => "original"

# -------------------------------------

class Object
  class << self
    def alias_method_no_copy(new_method, original_method)
      class_eval <<-EOF
        def #{new_method.to_s}(*opts)
          #{original_method.to_s}(*opts)
        end
      EOF
    end
  end
end

class A
  def foo
    puts 'original'
  end
end
 
class B < A
  alias_method_no_copy :bar, :foo
end
 
class A
  def foo
    puts 'modified'
  end
end

B.new.foo # => "modified"
B.new.bar # => "modified"