Is Borg really implemented right ?

[jpic]

I thought that the point of Borg was to allow subclassing. However, the implementation doesn't match expectations in this case:

class Borg:
    __shared_state = {}

    def __init__(self):
        self.__dict__ = self.__shared_state
        self.state = 'Running'

    def __str__(self):
        return self.state

instance0 = Borg()
instance1 = Borg()

instance0.state = 'Idle'

print instance1  # prints 'Idle', instead of 'Running', as expected

borg = Borg()
borg.state = 'Idle'


class YourBorg(Borg):
    pass

borg = YourBorg()
print borg  # prints 'Running' instead of 'Idle', **not** as expected

Are you sure that Borg supports setting attributes in the constructor ?

It looks like it defeats the purpose of Borg...

[faif]

You are right. Initializing variables inside the init function of the Borg doesn't work well. The updated example should demonstrate the Borg better. Thanks :)

[jpic]

Np, great repo !

[modasserbillah]

I know it's closed but the borg pattern still sets the state during init and the issue pointed out by @jpic stands. Reference

Am I missing something here?

[faif]

Hi.

It does set a state during init but that is not required. The state is changed later anyway, and subclassing works as expected (the state is modified also for subclasses). What is your concern?

[modasserbillah]

My concern is when an instance of the subclass is instantiated, the state gets changed. In my opinion, that should not be the case. When a new instance is created, the state should not change unless explicitly changed. Here's the argument from Alex Martelli : https://learning.oreilly.com/library/view/python-cookbook/0596001673/ch05s23.html

[faif]

I see your point. Setting the state in __init__ was used as an example but indeed it might not give the right idea. Feel free to make the change and I'll merge it.

[faif]

Fixed in #338