..
   Copyright 2009-2012 Ram Rachum. This work is licensed under a Creative
   Commons Attribution-ShareAlike 3.0 Unported License, with attribution to
   "Ram Rachum at ram.rachum.com" including link. The license may be obtained
   at http://creativecommons.org/licenses/by-sa/3.0/

.. _topics-caching-cached-type:

:class:`caching.CachedType`
===========================

A class that automatically caches its instances
-----------------------------------------------

Sometimes you define classes whose instances hold absolutely no state on them,
and are completey determined by the arguments passed to them. In these cases
using :class:`caching.CachedType` as a metaclass would cache class instances,
preventing more than one of them from being created:

   >>> from python_toolbox import caching
   >>>
   >>> class A(object):
   ...      __metaclass__ = caching.CachedType
   ...      def __init__(self, a=1, b=2):
   ...          self.a = a
   ...          self.b = b

Now every time you create an instance, it'll be cached:

   >>> my_instance = A(b=3)
   
And the next time you'll create an instance with the same arguments:

   >>> another_instance = A(b=3)
   
No instance will be actually created; the same instance from before will be used:

   >>> assert another_instance is my_instance

