Source code for ax.utils.common.result

# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

# pyre-strict

from __future__ import annotations

from abc import ABC, abstractmethod, abstractproperty

from typing import Any, Callable, cast, Generic, NoReturn, Optional, TypeVar, Union


T = TypeVar("T", covariant=True)
E = TypeVar("E", covariant=True)

U = TypeVar("U")
F = TypeVar("F")


[docs]class Result(Generic[T, E], ABC): """ A minimal implementation of a rusty Result monad. See https://doc.rust-lang.org/std/result/enum.Result.html for more information. """
[docs] @abstractmethod def is_ok(self) -> bool: pass
[docs] @abstractmethod def is_err(self) -> bool: pass
@abstractproperty def ok(self) -> Optional[T]: pass @abstractproperty def err(self) -> Optional[E]: pass @abstractproperty def value(self) -> Union[T, E]: pass
[docs] @abstractmethod def map(self, op: Callable[[T], U]) -> Result[U, E]: """ Maps a Result[T, E] to Result[U, E] by applying a function to a contained Ok value, leaving an Err value untouched. This function can be used to compose the results of two functions. """ pass
[docs] @abstractmethod def map_err(self, op: Callable[[E], F]) -> Result[T, F]: """ Maps a Result[T, E] to Result[T, F] by applying a function to a contained Err value, leaving an Ok value untouched. This function can be used to pass through a successful result while handling an error. """ pass
[docs] @abstractmethod def map_or(self, default: U, op: Callable[[T], U]) -> U: """ Returns the provided default (if Err), or applies a function to the contained value (if Ok). """ pass
[docs] @abstractmethod def map_or_else(self, default_op: Callable[[], U], op: Callable[[T], U]) -> U: """ Maps a Result[T, E] to U by applying fallback function default to a contained Err value, or function op to a contained Ok value. This function can be used to unpack a successful result while handling an error. """ pass
[docs] @abstractmethod def unwrap(self) -> T: """ Returns the contained Ok value. Because this function may raise an UnwrapError, its use is generally discouraged. Instead, prefer to handle the Err case explicitly, or call unwrap_or, unwrap_or_else, or unwrap_or_default. """ pass
[docs] @abstractmethod def unwrap_err(self) -> E: """ Returns the contained Err value. Because this function may raise an UnwrapError, its use is generally discouraged. Instead, prefer to handle the Err case explicitly, or call unwrap_or, unwrap_or_else, or unwrap_or_default. """ pass
[docs] @abstractmethod # pyre-ignore[46]: The type variable `Variable[T](covariant)` is covariant and # cannot be a parameter type. def unwrap_or(self, default: T) -> T: """Returns the contained Ok value or a provided default.""" pass
[docs] @abstractmethod def unwrap_or_else(self, op: Callable[[E], T]) -> T: """Returns the contained Ok value or computes it from a Callable.""" pass
[docs]class Ok(Generic[T, E], Result[T, E]): """ Contains the success value. """ _value: T def __init__(self, value: T) -> None: self._value = value def __repr__(self) -> str: return f"Ok({self._value})" # pyre-ignore[2]: Parameter `other` must have a type other than `Any`. def __eq__(self, other: Any) -> bool: return isinstance(other, Ok) and self._value == other._value def __hash__(self) -> int: return hash((True, self._value))
[docs] def is_ok(self) -> bool: return True
[docs] def is_err(self) -> bool: return False
@property def ok(self) -> T: return self._value @property def err(self) -> None: return None @property def value(self) -> T: return self._value
[docs] def map(self, op: Callable[[T], U]) -> Result[U, E]: return Ok(op(self._value))
[docs] def map_err(self, op: Callable[[E], F]) -> Result[T, F]: return cast(Result[T, F], self)
[docs] def map_or(self, default: U, op: Callable[[T], U]) -> U: return op(self._value)
[docs] def map_or_else(self, default_op: Callable[[], U], op: Callable[[T], U]) -> U: return op(self._value)
[docs] def unwrap(self) -> T: return self._value
[docs] def unwrap_err(self) -> NoReturn: raise UnwrapError(f"Tried to unwrap_err {self}.")
[docs] def unwrap_or(self, default: U) -> T: return self._value
[docs] def unwrap_or_else(self, op: Callable[[E], T]) -> T: return self._value
[docs]class Err(Generic[T, E], Result[T, E]): """ Contains the error value. """ def __init__(self, value: E) -> None: self._value = value def __repr__(self) -> str: return f"Err({self._value})" # pyre-ignore[2]: Parameter `other` must have a type other than `Any`. def __eq__(self, other: Any) -> bool: return isinstance(other, Err) and self._value == other._value def __hash__(self) -> int: return hash((False, self._value))
[docs] def is_ok(self) -> bool: return False
[docs] def is_err(self) -> bool: return True
@property def ok(self) -> None: return None @property def err(self) -> E: return self._value @property def value(self) -> E: return self._value
[docs] def map(self, op: Callable[[T], U]) -> Result[U, E]: return cast(Result[U, E], self)
[docs] def map_err(self, op: Callable[[E], F]) -> Result[T, F]: return Err(op(self._value))
[docs] def map_or(self, default: U, op: Callable[[T], U]) -> U: return default
[docs] def map_or_else(self, default_op: Callable[[], U], op: Callable[[T], U]) -> U: return default_op()
[docs] def unwrap(self) -> NoReturn: raise UnwrapError(f"Tried to unwrap {self}.")
[docs] def unwrap_err(self) -> E: return self._value
# pyre-ignore[46]: The type variable `Variable[T](covariant)` is covariant and # cannot be a parameter type.
[docs] def unwrap_or(self, default: T) -> T: return default
[docs] def unwrap_or_else(self, op: Callable[[E], T]) -> T: return op(self._value)
[docs]class UnwrapError(Exception): """ Exception that indicates something has gone wrong in an unwrap call. This should not happen in real world use and indicates a user has impropperly or unsafely used the Result abstraction. """ pass