Return factory from hook factory decorator functions

HISTORY.md

@@ -30,6 +30,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
   ([#748](https://github.com/python-attrs/cattrs/pull/748))
 - The [union passthrough strategy](https://catt.rs/en/stable/strategies.html#union-passthrough) now supports PEP 695 type aliases as union members.
   ([#753](https://github.com/python-attrs/cattrs/pull/753))
+- {meth}`BaseConverter.register_structure_hook_factory` and {meth}`BaseConverter.register_unstructure_hook_factory` now properly return the factory when used as decorators.
+  ([#724](https://github.com/python-attrs/cattrs/pull/724))
 
 ## 26.1.0 (2026-02-18)
 

src/cattrs/converters.py

@@ -443,6 +443,7 @@ def decorator(factory):
                     self._unstructure_func.register_func_list(
                         [(predicate, factory, True)]
                     )
+                return factory
 
             return decorator
 
@@ -581,6 +582,7 @@ def decorator(factory):
                     self._structure_func.register_func_list(
                         [(predicate, factory, True)]
                     )
+                return factory
 
             return decorator
         self._structure_func.register_func_list(

tests/test_typing_structure.md

@@ -102,3 +102,33 @@ converter = Converter()
 value: int = converter.structure("1", int)
 bad: str = converter.structure("1", int)  # mypy-error: [assignment]
 ```
+
+## Hook factory decorators preserve factory types
+
+```python
+from collections.abc import Callable
+from typing import Any
+
+from cattrs import Converter
+
+
+converter = Converter()
+
+
+def accepts_int(cl: Any) -> bool:
+    return cl is int
+
+
+@converter.register_unstructure_hook_factory(accepts_int)
+def unstructure_factory(cl: type[int]) -> Callable[[int], str]:
+    return str
+
+
+@converter.register_structure_hook_factory(accepts_int)
+def structure_factory(cl: type[int]) -> Callable[[str, type[int]], int]:
+    return lambda value, _: int(value)
+
+
+reveal_type(unstructure_factory)  # revealed: def (cl: type[int]) -> def (int) -> str
+reveal_type(structure_factory)  # revealed: def (cl: type[int]) -> def (str, type[int]) -> int
+```