From 7aa7fd566d3e138e3a644bd51ccdc3aa445869d5 Mon Sep 17 00:00:00 2001
From: Chris Withers <chris@simplistix.co.uk>
Date: Mon, 7 Jun 2010 15:56:35 +0000
Subject: A documented example of using Venusian to add your own decorator.

---
 docs/narr/hooks.rst | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

(limited to 'docs')

diff --git a/docs/narr/hooks.rst b/docs/narr/hooks.rst
index 678b9dbc3..97f68ab25 100644
--- a/docs/narr/hooks.rst
+++ b/docs/narr/hooks.rst
@@ -336,3 +336,86 @@ class :class:`repoze.bfg.traversal.TraversalContextURL` in the
 `traversal module
 <http://svn.repoze.org/repoze.bfg/trunk/repoze/bfg/traversal.py>`_ of
 the :term:`Repoze` Subversion repository.
+
+Registering your own decorators
+-------------------------------
+
+The decorators provided by :mod:`repoze.bfg`, such as
+:class:`~repoze.bfg.view.bfg_view`, neither molest the
+functions or classes they're decorating nor cause any side effects
+to happen until a :term:`scan` is performed.
+
+You may wish to have your own decorators that exhibit such
+behaviour. This is possible by using the :term:`Venusian` package in
+the same way that is used by :mod:`repoze.bfg`.
+
+For example, suppose you wanted to write a decorator that registered a
+particular function with a :term:`Zope Component Architecture`
+utility. Such a utility is likely only to be available once your
+application's configuration is at least partially completed. A normal
+decorator would fail as it would be executed before the
+configuration had even begun. 
+
+However, using :term:`Venusian`, the decorator could be written as
+follows:
+
+.. code-block:: python
+   :linenos:
+
+   import venusian
+   from zope.component import getSiteManager
+    
+   class registerFunction(object):
+        
+       def __init__(self,path):
+           self.path = path
+
+       def register(self,scanner,name,wrapped):
+           getSiteManager().getUtility(ISomething).register(
+               self.path,wrapped
+               )
+        
+       def __call__(self,wrapped):
+           venusian.attach(wrapped,self.register)
+           return wrapped
+    
+This decorator could then be used to register functions throughout
+your code:
+
+.. code-block:: python
+   :linenos:
+
+   @registerFunction('/some/path')
+   def my_function():
+      do_stuff()
+
+However, the utility would only be used when a :term:`scan` was
+performed, enabling you to set up the utility in advance:
+
+.. code-block:: python
+   :linenos:
+
+   from paste.httpserver import serve
+   from repoze.bfg.configuration import Configurator
+
+   class UtilityImplementation:
+
+       implements(ISomething)
+
+       def __init__(self):
+          self.registrations = {}
+
+       def register(self,path,callable_):
+          self.registrations[path]=callable_
+
+   if __name__ == '__main__':
+       config = Configurator()
+       config.begin()
+       config.registry.registerUtility(UtilityImplementation())
+       config.scan()
+       config.end()
+       app = config.make_wsgi_app()
+       serve(app, host='0.0.0.0')
+
+For full details, please read the `Venusian documentations
+<http://docs.repoze.org/venusian>`__.
-- 
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