What is the use of 'abstract_method'?

What is the use of 'abstract_method' in rails?

--Rahul

http://www.noobkit.com/show/ruby/gems/io/rio/module/abstract_method.html
defines it as:
"abstract_method(symbol, …) extends Module defines a method which
raises AbstractMethodCalled used in a base class to ensure that
subclasses define an implementation"

It is used to cap the parent class of an inheritance.

so if class Foo < Bar

and Bar.some_method you want it to have to be defined in all
subclasess (Foo and others...) you do like such:

class Bar
  def some_method
    abstract_method
  end
end

then all subclasses must implement some_method or it will complain
when being called (Note, untill it is called, everything is sweet,
this can casue bugs...)