ID Type

idtype.py

from dataclasses import field, dataclass


class ID:
    def __init__(self, value: int | None = None):
        self.value = value

    def set(self, value: int):
        if self.value is not None:
            raise ValueError("Value already exists")
        self.value = value

    def __eq__(self, other):
        if self.value is None:
            return self is other
        else:
            return type(self) == type(other) and self.value == other.value

    def __repr__(self):
        if self.value is None:
            return f"ID(tmp@{id(self)})"
        return f"{self.__class__.__qualname__}({self.value})"


@dataclass
class Parent:
    id: ID = field(default_factory=ID)


@dataclass
class Child:
    parent_id: ID


parent = Parent()
child = Child(parent_id=parent.id)
print(child, parent)
parent.id.set(100)
print(child, parent)