from typing import Any

__all__ = ["Undefined", "UndefinedType"]


class UndefinedType(ValueError):
    """Auxiliary class for creating the Undefined singleton."""

    def __repr__(self) -> str:
        return "Undefined"

    __str__ = __repr__

    def __hash__(self) -> int:
        return hash(UndefinedType)

    def __bool__(self) -> bool:
        return False

    def __eq__(self, other: Any) -> bool:
        return other is Undefined

    def __ne__(self, other: Any) -> bool:
        return not self == other


# Used to indicate undefined or invalid values (like "undefined" in JavaScript):
Undefined = UndefinedType()

Undefined.__doc__ = """Symbol for undefined values

This singleton object is used to describe undefined or invalid  values.
It can be used in places where you would use ``undefined`` in GraphQL.js.
"""