msgspec.Struct cannot be used together with abc

[777michael777]

Description

I am trying to create a Struct that is also an abstract class and run into the metaclass conflict.
Here's an example:

import msgspec
import abc


class Base(msgspec.Struct, metaclass=abc.ABCMeta):
    member: int

    @abc.abstractmethod
    def method(self) -> None:
        pass


class Subclass(Base):
    pass


a = Subclass(7)

When executing above code, I get

Traceback (most recent call last):
  File "x.py", line 5, in <module>
    class Base(msgspec.Struct, metaclass=abc.ABCMeta):
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

Also tried with not using the metaclass, but inherit Base from abc.ABC directly, with the same result.

[rafalkrupinski]

That makes sense, since msgspec.Struct brings its own metaclass. No abstract classes for us.

Funny, I tried to do the same thing just days ago, but I didn't know how to pass both metaclass parameters and two base classes. Didn't occur to me ABC brings a metaclass too.