Feature/transform

meiga/result.py

@@ -12,6 +12,7 @@
 TS = TypeVar("TS")  # Success Type
 TF = TypeVar("TF")  # Failure Type
 TEF = TypeVar("TEF")  # External Failure Type
+R = TypeVar("R")  # Recast expected type
 
 
 class Result(Generic[TS, TF]):
@@ -21,7 +22,12 @@ class Result(Generic[TS, TF]):
 
     __id__ = "__meiga_result_identifier__"
     __match_args__ = ("_value_success", "_value_failure")
-    __slots__ = ("_value_success", "_value_failure", "_is_success")
+    __slots__ = (
+        "_value_success",
+        "_value_failure",
+        "_is_success",
+        "_inner_transformer",
+    )
 
     def __init__(
         self,
@@ -31,6 +37,7 @@ def __init__(
         self._value_success = success
         self._value_failure = failure
         self._assert_values()
+        self._inner_transformer: Union[Callable[[Result], Any], None] = None
 
     def __repr__(self) -> str:
         status = "failure"
@@ -219,11 +226,11 @@ def handle(
 
         return self
 
-    def map(self, transform: Callable) -> None:
+    def map(self, mapper: Callable) -> None:
         """
         Returns a transformed result applying transform function applied to encapsulated value if this instance represents success or failure
         """
-        new_value = transform(self.value)
+        new_value = mapper(self.value)
         self.set_value(new_value)
 
     def assert_success(
@@ -255,3 +262,21 @@ def assert_failure(
         )
 
     value = property(get_value)
+
+    def set_transformer(self, transformer: Callable[["Result"], Any]):
+        """
+        Set a Callable transformer to be used with the `transform` method
+        """
+        self._inner_transformer = transformer
+
+    def transform(self, expected_type: Union[Type[R], None] = None) -> R:  # noqa
+        """
+        Transform the result with set transformer (Use `set_transformer` function to define it)
+        """
+        if not self._inner_transformer:
+            raise RuntimeError(
+                "Result object cannot be transformed as no transformer have been set yet. "
+                "Use result.set_transformer(callable) to add your transformer callable method"
+            )
+
+        return self._inner_transformer(self)

tests/unit/test_result_transform.py

@@ -0,0 +1,35 @@
+import pytest
+
+from meiga import Result, Success
+
+
+def transformer(result: Result):
+    return result.value
+
+
+@pytest.mark.unit
+def test_should_set_transformer_an_return_transformed_value():
+    result = Success("Hi")
+    result.set_transformer(transformer)
+
+    recast_result = result.transform()
+
+    assert recast_result == "Hi"
+
+
+@pytest.mark.unit
+def test_should_set_transformer_an_return_transformed_value_with_expected_type():
+    result = Success("Hi")
+    result.set_transformer(transformer)
+
+    recast_result = result.transform(expected_type=str)
+
+    assert recast_result == "Hi"
+
+
+@pytest.mark.unit
+def test_should_raise_an_error_when_transform_method_is_not_set():
+    result = Success("Hi")
+
+    with pytest.raises(RuntimeError):
+        result.transform()