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from abc import abstractmethod
from typing import Generic, TypeVar
_FirstType = TypeVar('_FirstType')
_SecondType = TypeVar('_SecondType')
_UnwrappableType = TypeVar('_UnwrappableType', bound='Unwrappable')
class Unwrappable(Generic[_FirstType, _SecondType]):
"""
Represents containers that can unwrap and return its wrapped value.
There are no aliases or ``UnwrappableN`` for ``Unwrappable`` interface.
Because it always uses two and just two types.
Not all types can be ``Unwrappable`` because we do require
to raise ``UnwrapFailedError`` if unwrap is not possible.
"""
__slots__ = ()
@abstractmethod
def unwrap(self: _UnwrappableType) -> _FirstType:
"""
Custom magic method to unwrap inner value from container.
Should be redefined for ones that actually have values.
And for ones that raise an exception for no values.
.. note::
As a part of the contract, failed ``unwrap`` calls
must raise :class:`returns.primitives.exceptions.UnwrapFailedError`
exception.
This method is the opposite of :meth:`~Unwrapable.failure`.
"""
@abstractmethod
def failure(self: _UnwrappableType) -> _SecondType:
"""
Custom magic method to unwrap inner value from the failed container.
.. note::
As a part of the contract, failed ``failure`` calls
must raise :class:`returns.primitives.exceptions.UnwrapFailedError`
exception.
This method is the opposite of :meth:`~Unwrapable.unwrap`.
"""
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