Re: [PR] GH-41668: [C++] Support cast kernel from list-like to (large) string [arrow]

["llama90 (via GitHub)" <gi...@apache.org>]

llama90 commented on code in PR #41831:
URL: https://github.com/apache/arrow/pull/41831#discussion_r1615198228


##########
cpp/src/arrow/compute/kernels/scalar_cast_test.cc:
##########
@@ -2476,54 +2508,137 @@ TEST(Cast, ListToFSL) {
                               CastOptions::Safe(fixed_size_list(int32(), 3))));
 }
 
-TEST(Cast, CastMap) {
-  const std::string map_json =
-      "[[[\"x\", 1], [\"y\", 8], [\"z\", 9]], [[\"x\", 6]], [[\"y\", 36]]]";
-  const std::string map_json_nullable =
-      "[[[\"x\", 1], [\"y\", null], [\"z\", 9]], null, [[\"y\", 36]]]";
+TEST_F(TestCastToString, ListToString) {
+  // Example with int32 list, large list, list view and large list view
+  const std::vector<std::pair<std::shared_ptr<DataType>, std::string>> list_types = {
+      {list(int32()), R"([
+  "list<item: int32>[1, 2]",
+  "list<item: int32>[3]",
+  "list<item: int32>[]"
+])"},
+      {large_list(int32()), R"([
+  "large_list<item: int32>[1, 2]",
+  "large_list<item: int32>[3]",
+  "large_list<item: int32>[]"
+])"},
+      {list_view(int32()), R"([
+  "list_view<item: int32>[1, 2]",
+  "list_view<item: int32>[3]",
+  "list_view<item: int32>[]"
+])"},
+      {large_list_view(int32()), R"([
+  "large_list_view<item: int32>[1, 2]",
+  "large_list_view<item: int32>[3]",
+  "large_list_view<item: int32>[]"
+])"}};
+
+  const std::string list_json = R"([[1, 2], [3], []])";
+
+  for (const auto& [list_type, expected_str] : list_types) {
+    CheckCastToString(list_type, list_json, expected_str);
+  }
+
+  // Example with nested list of int32.  To avoid further code duplication, the code for
+  // large_list, list_view, and large_list_view is omitted.
+  const std::vector<std::pair<std::shared_ptr<DataType>, std::string>> nested_list_types =
+      {{list(list(int32())), R"([
+  "list<item: list<item: int32>>[list<item: int32>[1, 2], list<item: int32>[3]]",
+  "list<item: list<item: int32>>[list<item: int32>[4]]",
+  "list<item: list<item: int32>>[list<item: int32>[]]",
+  "list<item: list<item: int32>>[]"
+])"}};
+
+  const std::string nested_list_json = R"([[[1, 2], [3]], [[4]], [[]], []])";
+
+  for (const auto& [nested_list_type, expected_nested_str] : nested_list_types) {
+    CheckCastToString(nested_list_type, nested_list_json, expected_nested_str);
+  }
+}
+
+class TestMapScalar : public TestCastToString {

Review Comment:
   Just as `TestMapScalar` was written for `MapType`, I wanted to write similar classes for `List` and `FixedSizeList`.
   
   However, I found it too extensive to address within this PR, so I only covered `MapType`. 
   
   It would be better to create a separate issue to handle this.



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