[GitHub] [iceberg] Fokko commented on a diff in pull request #4727: add VoidTransform

[GitBox <gi...@apache.org>]

Fokko commented on code in PR #4727:
URL: https://github.com/apache/iceberg/pull/4727#discussion_r867736811


##########
python/src/iceberg/transforms.py:
##########
@@ -249,6 +249,32 @@ def result_type(self, source: IcebergType) -> IcebergType:
         return StringType()
 
 
+class VoidTransform(Transform):
+    """A transform that always returns None"""
+
+    _instance = None
+
+    def __new__(cls):
+        if cls._instance is None:
+            cls._instance = super(VoidTransform, cls).__new__(cls)
+        return cls._instance
+
+    def __init__(self):
+        super().__init__("void", "transforms.always_null()")
+
+    def apply(self, value):

Review Comment:
   Related to https://github.com/apache/iceberg/pull/4728/
   ```suggestion
       def apply(self, value: Optional[S]) -> Optional[int]:
   ```



##########
python/src/iceberg/transforms.py:
##########
@@ -249,6 +249,32 @@ def result_type(self, source: IcebergType) -> IcebergType:
         return StringType()
 
 
+class VoidTransform(Transform):
+    """A transform that always returns None"""
+
+    _instance = None
+
+    def __new__(cls):

Review Comment:
   We could add a test for this:
   ```python
   def test_check_if_identical():
       assert transforms.always_null() is transforms.always_null()
   ```



##########
python/src/iceberg/transforms.py:
##########
@@ -249,6 +249,32 @@ def result_type(self, source: IcebergType) -> IcebergType:
         return StringType()
 
 
+class VoidTransform(Transform):
+    """A transform that always returns None"""
+
+    _instance = None
+
+    def __new__(cls):
+        if cls._instance is None:
+            cls._instance = super(VoidTransform, cls).__new__(cls)
+        return cls._instance
+
+    def __init__(self):
+        super().__init__("void", "transforms.always_null()")
+
+    def apply(self, value):
+        return None
+
+    def can_transform(self, target: IcebergType) -> bool:
+        return True
+
+    def result_type(self, source: IcebergType) -> IcebergType:
+        return source
+
+    def to_human_string(self, value) -> str:

Review Comment:
   ```suggestion
       def to_human_string(self, Optional[value]) -> str:
   ```



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