refactor: Update ArrowTypeList and related classes to use ArrowField for element type

Author: Marco

Arrow/Sources/Arrow/ArrowArray.swift

@@ -374,7 +374,7 @@ public class NestedArray: ArrowArray<[Any?]> {
             }
 
             self.children = [try ArrowArrayHolderImpl.loadArray(
-                listType.elementType,
+                listType.elementField.type,
                 with: arrowData.children[0]
             )]
 

Arrow/Sources/Arrow/ArrowArrayBuilder.swift

@@ -179,7 +179,7 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
 
     public override init(_ elementType: ArrowType) throws {
         self.valueBuilder = try ArrowArrayBuilders.loadBuilder(arrowType: elementType)
-        try super.init(ArrowTypeList(elementType))
+        try super.init(ArrowTypeList(ArrowField("item", type: elementType, isNullable: true)))
     }
 
     public override func append(_ values: [Any?]?) {
@@ -324,7 +324,7 @@ public class ArrowArrayBuilders {
             guard let listType = arrowType as? ArrowTypeList else {
                 throw ArrowError.invalid("Expected ArrowTypeList for \(arrowType.id)")
             }
-            return try ListArrayBuilder(listType.elementType)
+            return try ListArrayBuilder(listType.elementField.type)
         default:
             throw ArrowError.unknownType("Builder not found for arrow type: \(arrowType.id)")
         }

Arrow/Sources/Arrow/ArrowReaderHelper.swift

@@ -310,7 +310,8 @@ func findArrowType( // swiftlint:disable:this cyclomatic_complexity function_bod
             return ArrowType(ArrowType.ArrowUnknown)
         }
         let childType = findArrowType(childField)
-        return ArrowTypeList(childType)
+        let childFieldName = childField.name ?? "item"
+        return ArrowTypeList(ArrowField(childFieldName, type: childType, isNullable: childField.nullable))
     default:
         return ArrowType(ArrowType.ArrowUnknown)
     }

Arrow/Sources/Arrow/ArrowType.swift

@@ -174,12 +174,16 @@ public class ArrowTypeStruct: ArrowType {
 }
 
 public class ArrowTypeList: ArrowType {
-    let elementType: ArrowType
+    public let elementField: ArrowField
 
-    public init(_ elementType: ArrowType) {
-        self.elementType = elementType
+    public init(_ elementField: ArrowField) {
+        self.elementField = elementField
         super.init(ArrowType.ArrowList)
     }
+
+    public convenience init(_ elementType: ArrowType, nullable: Bool = true) {
+        self.init(ArrowField("item", type: elementType, isNullable: nullable))
+    }
 }
 
 public class ArrowType {
@@ -396,7 +400,7 @@ public class ArrowType {
                 throw ArrowError.invalid("Invalid struct type")
             case ArrowTypeId.list:
                 if let listType = self as? ArrowTypeList {
-                    return "+l" + (try listType.elementType.cDataFormatId)
+                    return "+l" + (try listType.elementField.type.cDataFormatId)
                 }
                 throw ArrowError.invalid("Invalid list type")
             default:

Arrow/Tests/ArrowTests/ArrayTests.swift

@@ -474,7 +474,7 @@ final class ArrayTests: XCTestCase { // swiftlint:disable:this type_body_length
     }
 
     func testListArrayNested() throws {
-        let innerListType = ArrowTypeList(ArrowType(ArrowType.ArrowInt32))
+        let innerListType = ArrowTypeList(ArrowField("item", type: ArrowType(ArrowType.ArrowInt32), isNullable: true))
         let outerListBuilder = try ListArrayBuilder(innerListType)
 
         guard let innerListBuilder = outerListBuilder.valueBuilder as? ListArrayBuilder else {