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Bind composite errors #1975

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Bind composite errors #1975

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e013e05
Bind composite error types
Dec 2, 2024
c9fdf6a
Bind composite error types, failure bind
Dec 2, 2024
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4 changes: 2 additions & 2 deletions returns/result.py
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Original file line number Diff line number Diff line change
Expand Up @@ -119,9 +119,9 @@ def bind(
self,
function: Callable[
[_ValueType],
Kind2['Result', _NewValueType, _ErrorType],
Kind2['Result', _NewValueType, _ErrorType | _NewErrorType],
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The problem with this approach is that it works with Exception subtypes, but it does not work if you have Result[int, int] and Result[int, str]

How would you compose these two objects? Result[int, int | str] might not make any sense.

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@edodo1337 edodo1337 Dec 3, 2024 •
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How would you compose these two objects? Result[int, int | str] might not make any sense.

Thank you for the review! I see your point, but isn’t int | str better than dealing with Any? At least with int | str, we can use pattern matching to handle each case explicitly.

],
) -> 'Result[_NewValueType, _ErrorType]':
) -> 'Result[_NewValueType, _ErrorType | _NewErrorType]':
"""
Composes successful container with a function that returns a container.

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15 changes: 15 additions & 0 deletions typesafety/test_result/test_construct_failure.yml
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Expand Up @@ -24,3 +24,18 @@
from returns.result import Failure

reveal_type(Failure(1).failure()) # N: Revealed type is "builtins.int"


- case: failure_bind_composite_error
disable_cache: false
main: |
from returns.result import Success, Failure, Result

def first_function(value: int) -> Result[str, ValueError]:
...

def second_function(value: str) -> Result[bool, KeyError]:
...

result = Failure(0).bind(first_function).bind(second_function)
reveal_type(result) # N: Revealed type is "returns.result.Result[builtins.bool, Union[builtins.int, builtins.ValueError, builtins.KeyError]]"
15 changes: 15 additions & 0 deletions typesafety/test_result/test_construct_success.yml
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Expand Up @@ -65,3 +65,18 @@
from returns.result import Success

reveal_type(Success(1).unwrap()) # N: Revealed type is "builtins.int"


- case: success_bind_composite_error
disable_cache: false
main: |
from returns.result import Success, Result

def returns_value_error(param: int) -> Result[str, ValueError]:
...

def returns_key_error(param: str) -> Result[str, KeyError]:
...

first: Result[int, Exception] = Success(1)
reveal_type(first.bind(returns_value_error).bind(returns_key_error)) # N: Revealed type is "returns.result.Result[builtins.str, Union[builtins.Exception, builtins.ValueError, builtins.KeyError]]"
2 changes: 1 addition & 1 deletion typesafety/test_result/test_result_type_cast.yml
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Expand Up @@ -109,7 +109,7 @@

first: Result[int, Exception]
second = first.bind(test)
reveal_type(second) # N: Revealed type is "returns.result.Result[builtins.int, builtins.Exception]"
reveal_type(second) # N: Revealed type is "returns.result.Result[builtins.int, Union[builtins.Exception, builtins.ValueError]]"


- case: result_correct_usage
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