Add unwrap convenience function (#47)

* Add unwrap convenience function

* Add test file

* Remove unsupported Python syntax

Author: AdrienVannson

docs/tutorial/messages.md

@@ -86,3 +86,24 @@ On Python 3.10 and later, it is also possible to use a `match` statement to find
 >>> find(Message())
 'No field set'
 ```
+
+## Unwrapping optional values
+
+In protobuf, fields are often marked as optional, either manually or because it is the default behavior of the protocol.
+If you care about type-checking, this can be tedious to handle as you need to make sure each field is not `None` before
+using, even when you know that the field will never be `None` is your application.
+
+```python
+# typing error: item "None" of "Message | None" has no attribute "field"
+message.msg_field.field
+```
+
+To simplify this, betterproto provides a convenience function: `unwrap`. This function takes an optional value, and
+returns the same value if it is not `None`. If the value is `None`, an error is raised.
+
+```python
+from betterproto2 import unwrap
+
+# no typing error!
+unwrap(message.msg_field).field
+```

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "betterproto2"
-version = "0.1.2"
+version = "0.1.3"
 description = "A better Protobuf / gRPC generator & library"
 authors = ["Adrien Vannson <[email protected]>", "Daniel G. Taylor <[email protected]>"]
 readme = "README.md"

src/betterproto2/__init__.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-__all__ = ["__version__", "check_compiler_version"]
+__all__ = ["__version__", "check_compiler_version", "unwrap"]
 
 import dataclasses
 import enum as builtin_enum
@@ -43,6 +43,8 @@
 from dateutil.parser import isoparse
 from typing_extensions import Self
 
+from betterproto2.utils import unwrap
+
 from ._types import T
 from ._version import __version__, check_compiler_version
 from .casing import (

src/betterproto2/utils.py

@@ -49,3 +49,24 @@ def __init__(self, func: Callable[[TT_co], T_co]):
 
     def __get__(self, instance: Any, type: TT_co) -> T_co:
         return self.__func__(type)
+
+
+T = TypeVar("T")
+
+
+def unwrap(x: T | None) -> T:
+    """
+    Unwraps an optional value, returning the value if it exists, or raises a ValueError if the value is None.
+
+    Args:
+        value (Optional[T]): The optional value to unwrap.
+
+    Returns:
+        T: The unwrapped value if it exists.
+
+    Raises:
+        ValueError: If the value is None.
+    """
+    if x is None:
+        raise ValueError("Can't unwrap a None value")
+    return x

tests/test_unwrap.py

@@ -0,0 +1,12 @@
+import pytest
+
+
+def test_unwrap() -> None:
+    from betterproto2 import unwrap
+    from tests.output_betterproto.unwrap import Message, NestedMessage
+
+    with pytest.raises(ValueError):
+        unwrap(Message().x)
+
+    msg = Message(x=NestedMessage())
+    assert msg.x == unwrap(msg.x)