timsaucer commented on code in PR #24365:
URL: https://github.com/apache/datafusion/pull/24365#discussion_r3785748145
##########
datafusion/functions-nested/src/replace.rs:
##########
@@ -367,6 +397,24 @@ impl ScalarUDFImpl for ArrayReplaceAll {
}
}
+/// Return field shared by `array_replace`, `array_replace_n` and
+/// `array_replace_all`: the input list type, except that its inner field is
+/// nullable whenever the replacement element may be null.
+fn replace_return_field(name: &str, arg_fields: &[FieldRef]) ->
Result<FieldRef> {
+ // `array` is at index 0 and `to` at index 2 for all three functions.
+ // `from` never contributes values to the output, so `to` is the only
+ // argument besides `array` that can affect the output's type.
+ let [array_field, _from_field, to_field, ..] = arg_fields else {
Review Comment:
Yes, exactly. `from` is only used to find the replacement match. It cannot
impact the output. The one place this may seem non-obvious is the case where
you have an array that is not nullable, and you have a `from` that is null and
a `to` that is not nullable. The output remains a non-nullable list.
```
> set datafusion.format.types_info = true;
0 row(s) fetched.
Elapsed 0.002 seconds.
> select array_replace(arrow_cast(column1, 'List(non-null Int64)'), NULL, 3)
from values (make_array(1, 2, 2));
+-------------------------------------------------------------------------------+
| array_replace(arrow_cast(column1,Utf8("List(non-null
Int64)")),NULL,Int64(3)) |
| List(non-null Int64)
|
+-------------------------------------------------------------------------------+
| [1, 2, 2]
|
+-------------------------------------------------------------------------------+
1 row(s) fetched.
```
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