Mixin support?

1. Mixining two classes that both inherit from pyrsistent.PClass fails:

import pyrsistent

class TimestampMixin(pyrsistent.PClass):
    created_at = pyrsistent.field()
    deleted_at = pyrsistent.field()
    updated_at = pyrsistent.field()

class IDMixin(pyrsistent.PClass):
    id = pyrsistent.field()

class UserEntity(IDMixin, TimestampMixin):
    pass

produces:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-808a9f22c5af> in <module>()
      9     id = pyrsistent.field()
     10
---> 11 class UserEntity(IDMixin, TimestampMixin):
     12     pass

~/.local/share/virtualenvs/server-hvEypR1j/lib/python3.6/site-packages/pyrsistent/_pclass.py in __new__(mcs, name, bases, dct)
     20             dct['__slots__'] += ('__weakref__',)
     21
---> 22         return super(PClassMeta, mcs).__new__(mcs, name, bases, dct)
     23
     24 _MISSING_VALUE = object()

TypeError: multiple bases have instance lay-out conflict

1. Using a mixin which doesn’t inherit from PClass doesn’t have it’s fields registered:

import pyrsistent

class TimestampMixin:
    created_at = pyrsistent.field()
    deleted_at = pyrsistent.field()
    updated_at = pyrsistent.field()

class IDMixin(pyrsistent.PClass):
    id = pyrsistent.field()

class UserEntity(IDMixin, TimestampMixin):
    pass

assert list(UserEntity._pclass_fields) == ['id']  # expecting: id, created_at, deleted_at, updated_at

Is there a suggested way to use mixins without falling back to: type('UserEntity', (pyrsistent.PClass,), namespace) where namespace is effectively a user-manifest mixin?

[tobgu]

That’s OK, I’ll leave the issue open, label it as an enhancement that someone can grab if they like. There are a bunch of similar issues that I myself don’t have time to work on but which I happily would accept PRs for.

[gelatinouscube42]

Is this behavior (of type 1 above) supported now?

I’ve been trying various tricks to get inheritance of fields to work, and this seems like it would have been an answer for my use case. Not sure where to start going about tooling around in the code itself to implement it if not yet there.