[Zope3-dev] Using classes as constants for security settings

[Steve Spicklemire]

Hi Steve,

	Good show! The only thing I can think of, is that this will be 
heavily used code, and could be a target for optimization later. But, 
with the new class/type unification, it doesn't seem likely that this 
will be a problem. It also seems unlikely that these classes will really 
"do" anything in their primary function as "constant state holders" so 
I'd say "check it in!"

-steve

On Sunday, February 17, 2002, at 08:58 AM, Steve Alexander wrote:

> I've been playing around with various ways of getting symbolic 
> constants that stay constant when you pickle and later unpickle them.
>
> Here's what I've come up with. This works as a replacement for 
> Zope/App/Security/Settings.py.
>
> ----
> """ Security setting constants """
>
> class PermissionSettingMetaClass(type):
>     def __init__(self, name, bases, namespace):
>         type.__init__(self, name, bases, namespace)
>         self._name=name
>
>     def __str__(self):
>         return "PermissionSetting: %s" % self._name
>
>     def _setDescription(self, description):
>         self._description=description
>
>     def getDescription(self):
>         return self._description
>
>
> class PermissionSetting(object):
>     __metaclass__=PermissionSettingMetaClass
>     def __init__(self):
>         raise TypeError, "Cannot instantiate PermissionSettings"
>
> # Explicit allow setting for permissions
> class Allow(PermissionSetting): pass
> Allow._setDescription("Explicit allow setting for permissions")
>
> # Explicit deny setting for permissions
> class Deny(PermissionSetting): pass
>
> # Unset constant that denotes no setting for permission and role
> class Unset(PermissionSetting): pass
>
> # Explicit assign setting for roles
> class Assign(PermissionSetting): pass
>
> # Explicit remove setting for roles
> class Remove(PermissionSetting): pass
>
> ----
>
> I have tested this, and several variations.
>
> There will only ever be one Allow class. The FQN of Allow is what gets 
> stored with pickled objects.
>
> However, we can add methods and descriptions to Allow, and other 
> permissions, by creating methods in PermissionSettingMetaClass.
>
> We can create __str__ and __repr__ methods on 
> PermissionSettingMetaClass to make the individual permissions say 
> something meaningful when printed.
>
>
> The choice for Settings.py is now as follows:
>
>   * Numbers for the values of Allow, Deny, Unset etc.
>
>   * Strings for the values of Allow, Deny, Unset etc., and we always
>     compare by equality, not identity
>
>   * Classes as symbolic constants, as above. Comparing by identity is
>     fine.
>
> Any opinions?
>
> --
> Steve Alexander
>
>
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