example_record_decorator.py

import msgspec
from typing import Callable


def record(func: Callable):
    annotations = func.__annotations__
    fields = [(k, v) for k, v in annotations.items()]

    # Define asdict method
    def asdict(self):
        return {f: getattr(self, f) for f in self.__struct_fields__}

    # Define replace method
    def replace(self, **new_data):
        """Return a new instance, replacing value as appropriate.
        Raise a TypeError if any unexpected keys are provided.
        """
        current_data = self.asdict()
        if diff := set(new_data.keys()).difference(current_data.keys()):
            raise TypeError(
                f"{type(self).__qualname__}.replace() called with unexpected arguments:"
                f"{', '.join(sorted(diff))}"
            )
        else:
            return type(self)(**(current_data | new_data))

    # Add the methods to the class namespace
    namespace = {"asdict": asdict, "replace": replace}

    return msgspec.defstruct(
        func.__name__, fields, forbid_unknown_fields=True, frozen=True, namespace=namespace
    )


# Usage:
@record
def Point(x: float, y: float):
    pass


p = Point(1.0, 1.0)
print(p.asdict())  # Output: {'x': 1.0, 'y': 1.0}
new_point = p.replace(y=2.0)
print(new_point.asdict())  # Output: {'x': 1.0, 'y': 2.0}