apacheGH-41945: [Swift] Add interface ArrowArrayHolderBuilder (apache…

…#41946)

### Rationale for this change

This change adds the implementation of the ArrowArrayHolderBuilder interface which allows appending to Arrays and completing them without needing the generic info.  This is needed for Nested types as well as for the Swift arrow Codable implementation.

### What changes are included in this PR?

Adding the interface and the implementation of the interface.

### Are these changes tested?

Yes, test has been added.

* GitHub Issue: apache#41945

Authored-by: Alva Bandy <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

swift/Arrow/Sources/Arrow/ArrowArrayBuilder.swift

@@ -17,7 +17,12 @@
 
 import Foundation
 
-public class ArrowArrayBuilder<T: ArrowBufferBuilder, U: ArrowArray<T.ItemType>> {
+public protocol ArrowArrayHolderBuilder {
+    func toHolder() throws -> ArrowArrayHolder
+    func appendAny(_ val: Any?)
+}
+
+public class ArrowArrayBuilder<T: ArrowBufferBuilder, U: ArrowArray<T.ItemType>>: ArrowArrayHolderBuilder {
     let type: ArrowType
     let bufferBuilder: T
     public var length: UInt {return self.bufferBuilder.length}
@@ -34,6 +39,10 @@ public class ArrowArrayBuilder<T: ArrowBufferBuilder, U: ArrowArray<T.ItemType>>
         self.bufferBuilder.append(val)
     }
 
+    public func appendAny(_ val: Any?) {
+        self.bufferBuilder.append(val as? T.ItemType)
+    }
+
     public func finish() throws -> ArrowArray<T.ItemType> {
         let buffers = self.bufferBuilder.finish()
         let arrowData = try ArrowData(self.type, buffers: buffers, nullCount: self.nullCount)
@@ -43,6 +52,10 @@ public class ArrowArrayBuilder<T: ArrowBufferBuilder, U: ArrowArray<T.ItemType>>
     public func getStride() -> Int {
         return self.type.getStride()
     }
+
+    public func toHolder() throws -> ArrowArrayHolder {
+        return try ArrowArrayHolderImpl(self.finish())
+    }
 }
 
 public class NumberArrayBuilder<T>: ArrowArrayBuilder<FixedBufferBuilder<T>, FixedArray<T>> {

swift/Arrow/Tests/ArrowTests/ArrayTests.swift

@@ -245,4 +245,30 @@ final class ArrayTests: XCTestCase {
         try checkHolderForType(ArrowType(ArrowType.ArrowBool))
         try checkHolderForType(ArrowType(ArrowType.ArrowString))
     }
-}
+
+    func testArrowArrayHolderBuilder() throws {
+        let uint8HBuilder: ArrowArrayHolderBuilder =
+            (try ArrowArrayBuilders.loadNumberArrayBuilder() as NumberArrayBuilder<UInt8>)
+        for index in 0..<100 {
+            uint8HBuilder.appendAny(UInt8(index))
+        }
+
+        let uint8Holder = try uint8HBuilder.toHolder()
+        XCTAssertEqual(uint8Holder.nullCount, 0)
+        XCTAssertEqual(uint8Holder.length, 100)
+
+        let stringHBuilder: ArrowArrayHolderBuilder =
+            (try ArrowArrayBuilders.loadStringArrayBuilder())
+         for index in 0..<100 {
+             if index % 10 == 9 {
+                 stringHBuilder.appendAny(nil)
+             } else {
+                 stringHBuilder.appendAny("test" + String(index))
+             }
+         }
+
+        let stringHolder = try stringHBuilder.toHolder()
+        XCTAssertEqual(stringHolder.nullCount, 10)
+        XCTAssertEqual(stringHolder.length, 100)
+    }
+ }