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docs: update readme to mention usage of isinstance to narrow types #177

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Jan 30, 2024
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docs: update readme to mention usage of isinstance to narrow types #177

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21 changes: 21 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -156,6 +156,27 @@ False
True
```

The benefit of `isinstance` is better type checking that type guards currently
do not offer,

```python
res1: Result[int, str] = some_result()
if isinstance(res1, Err):
print("Error...:", res1.err_value) # res1 is narrowed to an Err
return
res1.ok()

res2: Result[int, str] = some_result()
if res1.is_err():
print("Error...:", res2.err_value) # res1 is NOT narrowed to an Err here
return
res1.ok()
```

There is a proposed [PEP 724 – Stricter Type Guards](https://peps.python.org/pep-0724/)
which may allow the `is_ok` and `is_err` type guards to work as expected in
future versions of Python.

Convert a `Result` to the value or `None`:

``` python
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