Point well taken, and indeed a brilliant solution. Thank you I V for
demonstrating so clearly.
I V wrote:
> On Mon, 26 Jun 2006 19:40:52 -0700, digitalorganics wrote:
> > A misuse of inheritance eh? Inheritance, like other language features,
> > is merely a tool. I happen to be using this tool to have my virtual
> > persons change roles at different points in their lifetime, as many
> > real people tend to do. Thus, at these points, B is indeed an A. What a
> > person is, whether in real life or in my program, is not static and
> > comes into definition uniquely for each moment (micro-moment, etc.) of
> > existence. Now, please, I have no intention of carrying the
> > conversation in such a silly direction, I wasn't inviting a discussion
> > on philosophy or some such. I seek to work the tools to my needs, not
> > the other way around.
>
> But thinking about the problem in the vocabulary provided by the
> programming language can be helpful in coming up with a solution. If
> inheritance tells you what an object _is_, and membership tells you what a
> role _has_, and a role is something that a person has, that suggests
> that an implementation where roles are members of a person might be
> simpler than trying to use inheritance. Like, for instance:
>
> class Role(object):
> def __init__(self, person):
> self.person = person
>
>
> class Worker(Role):
> def do_work(self):
> print self.name, "is working"
>
>
> class Employer(Role):
>
> def __init__(self, person):
> Role.__init__(self, person)
> self.employees = []
>
>
> def add_employee(self, worker):
> self.employees.append(worker)
>
>
> def boss_people_around(self):
> for employee in employees:
> print self.name, "is telling", employee.name, "what to
> do"
>
>
> class Person(object):
>
> def __init__(self, name):
> self.roles = []
> self.name = name
>
>
> def add_role(self, role_class):
> self.roles.append(role_class(self))
>
>
> def forward_to_role(self, attr):
> for role in self.roles:
> try:
> return getattr(role, attr)
> except AttributeError:
> pass
> raise AttributeError(attr)
>
>
> def __getattr__(self, attr):
> self.forward_to_role(attr)
>
>
> bill = Person('Bill')
> bill.add_role(Worker)
>
> bob = Person('Bob')
> bob.add_role(Employer)
>
> bill.work()
> bob.boss_people_around()
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