Rails - Jul 2006 - Should I use exclamation marks for methods that change associations?

I''ve been getting some good feedback on the Authorization plugin
(http://www.writertopia.com/developers/authorization). Josh Susser
suggested I use exclamation marks when I''m setting roles. The basic
ways of setting roles uses the #has_role, #has_no_role, #accepts_role,
and #accepts_no_role methods:

        user.has_role ''site_admin''
        user.has_role ''moderator'', group
        user.has_no_role ''site_admin''
        user.has_role ''member'', Group
        a_model.accepts_role ''moderator'', user
        a_model.accepts_no_role ''moderator'', user
        Model.accepts_role ''class moderator'', user

With the new dynamic methods, we give the user-like model some flexibility:

  user.is_moderator_of group  --> sets user to have role
"moderator"
for object group.
  user.is_administrator       --> sets user to have role
"administrator" not really tied to any object.
  user.is_eligible_for award  --> sets user to have role "eligible"
for object award.

In the discussions I''ve read on proper use of exclamation marks, some
say it should only be used when destructive effects are not obvious
from the name. So #delete doesn''t need an exclamation mark.
Exclamation marks might also show when the given object is modified.
In the case of roles, a " user.has_role! foo" won''t change
the user
object but could possible change the join table and the Role table.

On the other hand, I''m leaning toward adding the exclamation mark
because it clarifies the difference between methods.

        user.has_role! ''site_admin''
        user.has_role? ''site_admin''
        user.is_moderator_of_what
        user.is_moderator_of! group
        user.is_moderator_of? group
        group.has_moderators
        group.has_moderators?

The "group.has_moderators" case shows how there might be some
ambiguity. Methods like has_blahs on models return an array of user
objects that have role "blah". The has_moderators method
doesn''t set a
role, but it might be clear because saying some model "has moderators"
doesn''t mean you are setting those moderators.

Comments are appreciated.
-Bill