From 77dda93a89da93571c4752a739c0493e957bb876 Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Fri, 31 Oct 2025 14:43:41 +0800
Subject: [PATCH 1/6] AsString merged into AnyArrowArray

---
 Sources/Arrow/ArrowArray.swift   |  7 +++--
 Sources/Arrow/ChunkedArray.swift |  6 +---
 Tests/ArrowTests/IPCTests.swift  | 50 +++++++++++++++-----------------
 3 files changed, 29 insertions(+), 34 deletions(-)

diff --git a/Sources/Arrow/ArrowArray.swift b/Sources/Arrow/ArrowArray.swift
index f9de931..559c124 100644
--- a/Sources/Arrow/ArrowArray.swift
+++ b/Sources/Arrow/ArrowArray.swift
@@ -24,12 +24,13 @@ public protocol AnyArrowArray {
   var bufferData: [Data] { get }
   var bufferDataSizes: [Int] { get }
   func asAny(_ index: UInt) -> Any?
+  func asString(_ index: UInt) -> String
 }
 
 // MARK: - Core Protocol
 
 /// The interface for Arrow array types.
-public protocol ArrowArray<ItemType>: AsString, AnyArrowArray {
+public protocol ArrowArray<ItemType>: AnyArrowArray {
   associatedtype ItemType
   var arrowData: ArrowData { get }
   init(_ arrowData: ArrowData) throws(ArrowError)
@@ -451,7 +452,7 @@ public struct NestedArray: ArrowArray, AnyArrowArray {
         switch item {
         case nil:
           output.append("null")
-        case let asStringItem as AsString:
+        case let asStringItem as AnyArrowArray:
           output.append(asStringItem.asString(0))
         case let someItem?:
           output.append("\(someItem)")
@@ -466,7 +467,7 @@ public struct NestedArray: ArrowArray, AnyArrowArray {
       var output = "{"
       if let children = self.children {
         let parts = children.compactMap { child in
-          (child as? AsString)?.asString(index)
+          child.asString(index)
         }
         output.append(parts.joined(separator: ","))
       }
diff --git a/Sources/Arrow/ChunkedArray.swift b/Sources/Arrow/ChunkedArray.swift
index bc8fde0..182caf0 100644
--- a/Sources/Arrow/ChunkedArray.swift
+++ b/Sources/Arrow/ChunkedArray.swift
@@ -14,10 +14,6 @@
 
 import Foundation
 
-public protocol AsString {
-  func asString(_ index: UInt) -> String
-}
-
 public class ChunkedArrayHolder {
   public let type: ArrowType
   public let length: UInt
@@ -85,7 +81,7 @@ public class ChunkedArrayHolder {
   }
 }
 
-public class ChunkedArray<T>: AsString {
+public class ChunkedArray<T> {
   public let arrays: [any ArrowArray<T>]
   public let type: ArrowType
   public let nullCount: UInt
diff --git a/Tests/ArrowTests/IPCTests.swift b/Tests/ArrowTests/IPCTests.swift
index 6614627..83abf3a 100644
--- a/Tests/ArrowTests/IPCTests.swift
+++ b/Tests/ArrowTests/IPCTests.swift
@@ -71,10 +71,10 @@ func checkBoolRecordBatch(
     #expect(recordBatch.schema.fields[1].type == .utf8)
     for index in 0..<recordBatch.length {
       let column = recordBatch.columns[0]
-      guard let str = column as? AsString else {
-        throw .invalid("Could not cast column to AsString")
-      }
-      let val = "\(str.asString(index))"
+//      guard let str = column as? AsString else {
+//        throw .invalid("Could not cast column to AsString")
+//      }
+      let val = "\(column.asString(index))"
       if index == 0 || index == 4 {
         #expect(val == "true")
       } else if index == 2 {
@@ -118,11 +118,11 @@ func checkStructRecordBatch(
     #expect(fields[0].type == .utf8)
     #expect(fields[1].type == .boolean)
     let column = recordBatch.columns[0]
-    guard let str = column as? AsString else {
-      throw .runtimeError("String array is nil")
-    }
-    #expect("\(str.asString(0))" == "{0,false}")
-    #expect("\(str.asString(1))" == "{1,true}")
+//    guard let str = column else {
+//      throw .runtimeError("String array is nil")
+//    }
+    #expect("\(column.asString(0))" == "{0,false}")
+    #expect("\(column.asString(1))" == "{1,true}")
     #expect(column.asAny(2) == nil)
   }
   return recordBatches
@@ -277,15 +277,15 @@ struct IPCStreamReaderTests {
           #expect(recordBatch.schema.fields[4].type == .float32)
           let columns = recordBatch.columns
           #expect(columns[0].nullCount == 2)
-          let dateVal = "\((columns[2]  as! AsString).asString(0))"
+          let dateVal = "\((columns[2]).asString(0))"
           #expect(dateVal == "2014-09-10 00:00:00 +0000")
-          let stringVal = "\((columns[1]  as! AsString).asString(1))"
+          let stringVal = "\((columns[1]).asString(1))"
           #expect(stringVal == "test22")
-          let uintVal = "\((columns[0]  as! AsString).asString(0))"
+          let uintVal = "\((columns[0]).asString(0))"
           #expect(uintVal == "10")
-          let stringVal2 = "\((columns[1]  as! AsString).asString(3))"
+          let stringVal2 = "\((columns[1]).asString(3))"
           #expect(stringVal2 == "test44")
-          let uintVal2 = "\((columns[0]  as! AsString).asString(3))"
+          let uintVal2 = "\((columns[0]).asString(3))"
           #expect(uintVal2 == "44")
         }
       case .failure(let error):
@@ -323,8 +323,7 @@ struct IPCFileReaderTests {
         recordBatch.schema.fields[1].type == .utf8)
       for index in 0..<recordBatch.length {
         let column = recordBatch.columns[1]
-        let str = column as! AsString
-        let val = "\(str.asString(index))"
+        let val = "\(column.asString(index))"
         if index != 1 {
           #expect(!val.isEmpty)
         } else {
@@ -430,15 +429,15 @@ struct IPCFileReaderTests {
           #expect(recordBatch.schema.fields[4].type == .float32)
           let columns = recordBatch.columns
           #expect(columns[0].nullCount == 2)
-          let dateVal = "\((columns[2]  as! AsString).asString(0))"
+          let dateVal = "\(columns[2].asString(0))"
           #expect(dateVal == "2014-09-10 00:00:00 +0000")
-          let stringVal = "\((columns[1]  as! AsString).asString(1))"
+          let stringVal = "\(columns[1].asString(1))"
           #expect(stringVal == "test22")
-          let uintVal = "\((columns[0]  as! AsString).asString(0))"
+          let uintVal = "\(columns[0].asString(0))"
           #expect(uintVal == "10")
-          let stringVal2 = "\((columns[1]  as! AsString).asString(3))"
+          let stringVal2 = "\(columns[1].asString(3))"
           #expect(stringVal2 == "test44")
-          let uintVal2 = "\((columns[0]  as! AsString).asString(3))"
+          let uintVal2 = "\(columns[0].asString(3))"
           #expect(uintVal2 == "44")
         }
       case .failure(let error):
@@ -572,7 +571,7 @@ struct IPCFileReaderTests {
           let columns = recordBatch.columns
           #expect(columns[0].nullCount == 1)
           #expect(columns[0].asAny(1) == nil)
-          let structVal = "\((columns[0]  as? AsString)!.asString(0))"
+          let structVal = "\(columns[0].asString(0))"
           #expect(
             structVal == "{true,1,2,3,4,5,6,7,8,9.9,10.1,11,12,\(currentDate)}")
           let nestedArray = (recordBatch.columns[0] as? NestedArray)!
@@ -625,7 +624,7 @@ struct IPCFileReaderTests {
         #expect(recordBatch.length == 4)
         let columns = recordBatch.columns
         let stringVal =
-          "\((columns[0]  as! AsString).asString(1))"
+          "\(columns[0].asString(1))"
         #expect(stringVal == "test22")
       case .failure(let error):
         throw error
@@ -659,11 +658,10 @@ struct IPCFileReaderTests {
         let recordBatch = result.batches[0]
         #expect(recordBatch.length == 4)
         let columns = recordBatch.columns
-        let stringVal =
-          "\((columns[0]  as! AsString).asString(0))"
+        let stringVal = "\(columns[0].asString(0))"
         #expect(stringVal == "12345678")
         let stringVal2 =
-          "\((columns[1]  as! AsString).asString(3))"
+          "\(columns[1].asString(3))"
         #expect(stringVal2 == "3")
       case .failure(let error):
         throw error

From e60219f1c19d329bdb34e07efcab6f8c57cde6f5 Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Fri, 31 Oct 2025 17:08:06 +0800
Subject: [PATCH 2/6] Gather FlatBuffers utilities into one place.

---
 Sources/Arrow/ArrowArray.swift                |   7 +-
 ...rrowArray.swift => ArrowArrayLoader.swift} |   1 -
 Sources/Arrow/ArrowReader.swift               |   7 +
 Sources/Arrow/ArrowReaderHelper.swift         | 189 ++----------------
 Sources/Arrow/FlatBuffersHelpers.swift        | 165 +++++++++++++++
 5 files changed, 189 insertions(+), 180 deletions(-)
 rename Sources/Arrow/{AnyArrowArray.swift => ArrowArrayLoader.swift} (97%)
 create mode 100644 Sources/Arrow/FlatBuffersHelpers.swift

diff --git a/Sources/Arrow/ArrowArray.swift b/Sources/Arrow/ArrowArray.swift
index 559c124..0405e85 100644
--- a/Sources/Arrow/ArrowArray.swift
+++ b/Sources/Arrow/ArrowArray.swift
@@ -38,6 +38,7 @@ public protocol ArrowArray<ItemType>: AnyArrowArray {
 }
 
 // MARK: - Default Implementations
+
 extension ArrowArray {
 
   public var nullCount: UInt {
@@ -189,8 +190,7 @@ public struct Date32Array: ArrowArray {
     let byteOffset = self.arrowData.stride * Int(index)
     let milliseconds = self.arrowData.buffers[1].rawPointer.advanced(
       by: byteOffset
-    ).load(
-      as: UInt32.self)
+    ).load(as: UInt32.self)
     return Date(timeIntervalSince1970: TimeInterval(milliseconds * 86400))
   }
 }
@@ -210,8 +210,7 @@ public struct Date64Array: ArrowArray {
     let byteOffset = self.arrowData.stride * Int(index)
     let milliseconds = self.arrowData.buffers[1].rawPointer.advanced(
       by: byteOffset
-    ).load(
-      as: UInt64.self)
+    ).load(as: UInt64.self)
     return Date(timeIntervalSince1970: TimeInterval(milliseconds / 1000))
   }
 }
diff --git a/Sources/Arrow/AnyArrowArray.swift b/Sources/Arrow/ArrowArrayLoader.swift
similarity index 97%
rename from Sources/Arrow/AnyArrowArray.swift
rename to Sources/Arrow/ArrowArrayLoader.swift
index b27c33b..56dbf43 100644
--- a/Sources/Arrow/AnyArrowArray.swift
+++ b/Sources/Arrow/ArrowArrayLoader.swift
@@ -13,7 +13,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// FIXME: Temporary to support holder refactor
 struct ArrowArrayLoader {
   public static func loadArray(
     _ arrowType: ArrowType,
diff --git a/Sources/Arrow/ArrowReader.swift b/Sources/Arrow/ArrowReader.swift
index 8891ec1..006c165 100644
--- a/Sources/Arrow/ArrowReader.swift
+++ b/Sources/Arrow/ArrowReader.swift
@@ -544,4 +544,11 @@ public struct ArrowReader: Sendable {
         .unknownError("Unhandled header type: \(message.headerType)"))
     }
   }
+  
+  func validateFileData(_ data: Data) -> Bool {
+    let markerLength = fileMarker.count
+    let startString = data[..<markerLength]
+    let endString = data[(data.count - markerLength)...]
+    return startString == fileMarker && endString == fileMarker
+  }
 }
diff --git a/Sources/Arrow/ArrowReaderHelper.swift b/Sources/Arrow/ArrowReaderHelper.swift
index f6ae486..08cd49e 100644
--- a/Sources/Arrow/ArrowReaderHelper.swift
+++ b/Sources/Arrow/ArrowReaderHelper.swift
@@ -38,27 +38,6 @@ private func makeStringHolder(
   return .success(StringArray(arrowData))
 }
 
-private func makeDateHolder(
-  _ field: ArrowField,
-  buffers: [ArrowBuffer],
-  nullCount: UInt
-) -> Result<AnyArrowArray, ArrowError> {
-  if field.type == .date32 {
-    let arrowData = ArrowData(
-      field.type,
-      buffers: buffers,
-      nullCount: nullCount
-    )
-    return .success(Date32Array(arrowData))
-  }
-  let arrowData = ArrowData(
-    field.type,
-    buffers: buffers,
-    nullCount: nullCount
-  )
-  return .success(Date64Array(arrowData))
-}
-
 private func makeBoolHolder(
   _ buffers: [ArrowBuffer],
   nullCount: UInt
@@ -193,8 +172,20 @@ func makeArrayHolder(
     return makeStringHolder(buffers, nullCount: nullCount)
   case .binary:
     return makeBinaryHolder(buffers, nullCount: nullCount)
-  case .date32, .date64:
-    return makeDateHolder(field, buffers: buffers, nullCount: nullCount)
+  case .date32:
+    let arrowData = ArrowData(
+      field.type,
+      buffers: buffers,
+      nullCount: nullCount
+    )
+    return .success(Date32Array(arrowData))
+  case .date64:
+    let arrowData = ArrowData(
+      field.type,
+      buffers: buffers,
+      nullCount: nullCount
+    )
+    return .success(Date64Array(arrowData))
   case .time32:
     let arrowData = ArrowData(
       field.type, buffers: buffers, nullCount: nullCount)
@@ -226,159 +217,7 @@ func makeArrayHolder(
   }
 }
 
-func makeBuffer(
-  _ buffer: Buffer, fileData: Data,
-  length: UInt, messageOffset: Int64
-) -> ArrowBuffer {
-  let startOffset = messageOffset + buffer.offset
-  let endOffset = startOffset + buffer.length
-  let bufferData = [UInt8](fileData[startOffset..<endOffset])
-  return ArrowBuffer.createBuffer(bufferData, length: length)
-}
 
-func isFixedPrimitive(_ type: FlatType) -> Bool {
-  switch type {
-  case .int, .bool, .floatingpoint, .date, .time, .timestamp:
-    return true
-  default:
-    return false
-  }
-}
-
-func findArrowType(_ field: FlatField) throws(ArrowError) -> ArrowType {
-  let type = field.typeType
-  switch type {
-  case .int:
-    guard let intType = field.type(type: FlatInt.self) else {
-      throw .invalid("Could not get integer type from \(field)")
-    }
-    let bitWidth = intType.bitWidth
-    if bitWidth == 8 {
-      if intType.isSigned {
-        return .int8
-      } else {
-        return .uint8
-      }
-    }
-    if bitWidth == 16 {
-      return intType.isSigned ? .int16 : .uint16
-    }
-    if bitWidth == 32 {
-      return intType.isSigned ? .int32 : .uint32
-    }
-    if bitWidth == 64 {
-      return intType.isSigned ? .int64 : .uint64
-    }
-    throw .invalid("Unhandled integer bit width: \(bitWidth)")
-  case .bool:
-    return .boolean
-  case .floatingpoint:
-    guard let floatType = field.type(type: FloatingPoint.self) else {
-      throw .invalid("Could not get floating point type from field")
-    }
-    switch floatType.precision {
-    case .half:
-      return .float16
-    case .single:
-      return .float32
-    case .double:
-      return .float64
-    }
-  case .utf8:
-    return .utf8
-  case .binary:
-    return .binary
-  case .date:
-    guard let dateType = field.type(type: FlatDate.self) else {
-      throw .invalid("Could not get date type from field")
-    }
-    if dateType.unit == .day {
-      return .date32
-    }
-    return .date64
-  case .time:
-    guard let timeType = field.type(type: FlatTime.self) else {
-      throw .invalid("Could not get time type from field")
-    }
-    if timeType.unit == .second || timeType.unit == .millisecond {
-      return .time32(
-        timeType.unit == .second ? .second : .millisecond
-      )
-    }
-    return .time64(
-      timeType.unit == .microsecond ? .microsecond : .nanosecond
-    )
-  case .timestamp:
-    guard let timestampType = field.type(type: FlatTimestamp.self) else {
-      throw .invalid("Could not get timestamp type from field")
-    }
-    let arrowUnit: TimeUnit
-    switch timestampType.unit {
-    case .second:
-      arrowUnit = .second
-    case .millisecond:
-      arrowUnit = .millisecond
-    case .microsecond:
-      arrowUnit = .microsecond
-    case .nanosecond:
-      arrowUnit = .nanosecond
-    }
-    let timezone = timestampType.timezone
-    return .timestamp(arrowUnit, timezone)
-  case .struct_:
-    guard field.type(type: FlatStruct.self) != nil else {
-      throw .invalid("Could not get struct type from field")
-    }
-    var fields: [ArrowField] = []
-    for index in 0..<field.childrenCount {
-      guard let childField = field.children(at: index) else {
-        throw .invalid("Could not get child at index: \(index) ofrom struct")
-      }
-      let childType = try findArrowType(childField)
-      guard let name = childField.name else {
-        throw .invalid("Could not get name of child field")
-      }
-      fields.append(
-        ArrowField(
-          name: name,
-          dataType: childType,
-          isNullable: childField.nullable
-        )
-      )
-    }
-    return .strct(fields)
-  case .list:
-    guard field.childrenCount == 1, let childField = field.children(at: 0)
-    else {
-      throw .invalid("Expected list field to have exactly one child")
-    }
-    let childType = try findArrowType(childField)
-    guard let name = childField.name else {
-      throw .invalid("Could not get name of child field")
-    }
-    let arrowField = ArrowField(
-      name: name,
-      dataType: childType,
-      isNullable: childField.nullable
-    )
-    return .list(arrowField)
-  default:
-    throw .invalid("Unhandled field type: \(field.typeType)")
-  }
-}
-
-func validateBufferIndex(_ recordBatch: FlatRecordBatch, index: Int32) throws {
-  if index >= recordBatch.buffersCount {
-    throw ArrowError.outOfBounds(index: Int64(index))
-  }
-}
-
-func validateFileData(_ data: Data) -> Bool {
-  let markerLength = fileMarker.count
-  let startString = data[..<markerLength]
-  let endString = data[(data.count - markerLength)...]
-  return startString == fileMarker && endString == fileMarker
-}
 
 func getUInt32(_ data: Data, offset: Int) -> UInt32 {
   let token = data.withUnsafeBytes { rawBuffer in
diff --git a/Sources/Arrow/FlatBuffersHelpers.swift b/Sources/Arrow/FlatBuffersHelpers.swift
new file mode 100644
index 0000000..6fcd3a1
--- /dev/null
+++ b/Sources/Arrow/FlatBuffersHelpers.swift
@@ -0,0 +1,165 @@
+// Copyright 2025 The Apache Software Foundation
+// Copyright 2025 The Columnar-Swift Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+
+func makeBuffer(
+  _ buffer: Buffer,
+  fileData: Data,
+  length: UInt,
+  messageOffset: Int64
+) -> ArrowBuffer {
+  let startOffset = messageOffset + buffer.offset
+  let endOffset = startOffset + buffer.length
+  let bufferData = [UInt8](fileData[startOffset..<endOffset])
+  return ArrowBuffer.createBuffer(bufferData, length: length)
+}
+
+func isFixedPrimitive(_ type: FlatType) -> Bool {
+  switch type {
+  case .int, .bool, .floatingpoint, .date, .time, .timestamp:
+    return true
+  default:
+    return false
+  }
+}
+
+func findArrowType(_ field: FlatField) throws(ArrowError) -> ArrowType {
+  let type = field.typeType
+  switch type {
+  case .int:
+    guard let intType = field.type(type: FlatInt.self) else {
+      throw .invalid("Could not get integer type from \(field)")
+    }
+    let bitWidth = intType.bitWidth
+    if bitWidth == 8 {
+      if intType.isSigned {
+        return .int8
+      } else {
+        return .uint8
+      }
+    }
+    if bitWidth == 16 {
+      return intType.isSigned ? .int16 : .uint16
+    }
+    if bitWidth == 32 {
+      return intType.isSigned ? .int32 : .uint32
+    }
+    if bitWidth == 64 {
+      return intType.isSigned ? .int64 : .uint64
+    }
+    throw .invalid("Unhandled integer bit width: \(bitWidth)")
+  case .bool:
+    return .boolean
+  case .floatingpoint:
+    guard let floatType = field.type(type: FloatingPoint.self) else {
+      throw .invalid("Could not get floating point type from field")
+    }
+    switch floatType.precision {
+    case .half:
+      return .float16
+    case .single:
+      return .float32
+    case .double:
+      return .float64
+    }
+  case .utf8:
+    return .utf8
+  case .binary:
+    return .binary
+  case .date:
+    guard let dateType = field.type(type: FlatDate.self) else {
+      throw .invalid("Could not get date type from field")
+    }
+    if dateType.unit == .day {
+      return .date32
+    }
+    return .date64
+  case .time:
+    guard let timeType = field.type(type: FlatTime.self) else {
+      throw .invalid("Could not get time type from field")
+    }
+    if timeType.unit == .second || timeType.unit == .millisecond {
+      return .time32(
+        timeType.unit == .second ? .second : .millisecond
+      )
+    }
+    return .time64(
+      timeType.unit == .microsecond ? .microsecond : .nanosecond
+    )
+  case .timestamp:
+    guard let timestampType = field.type(type: FlatTimestamp.self) else {
+      throw .invalid("Could not get timestamp type from field")
+    }
+    let arrowUnit: TimeUnit
+    switch timestampType.unit {
+    case .second:
+      arrowUnit = .second
+    case .millisecond:
+      arrowUnit = .millisecond
+    case .microsecond:
+      arrowUnit = .microsecond
+    case .nanosecond:
+      arrowUnit = .nanosecond
+    }
+    let timezone = timestampType.timezone
+    return .timestamp(arrowUnit, timezone)
+  case .struct_:
+    guard field.type(type: FlatStruct.self) != nil else {
+      throw .invalid("Could not get struct type from field")
+    }
+    var fields: [ArrowField] = []
+    for index in 0..<field.childrenCount {
+      guard let childField = field.children(at: index) else {
+        throw .invalid("Could not get child at index: \(index) ofrom struct")
+      }
+      let childType = try findArrowType(childField)
+      guard let name = childField.name else {
+        throw .invalid("Could not get name of child field")
+      }
+      fields.append(
+        ArrowField(
+          name: name,
+          dataType: childType,
+          isNullable: childField.nullable
+        )
+      )
+    }
+    return .strct(fields)
+  case .list:
+    guard field.childrenCount == 1, let childField = field.children(at: 0)
+    else {
+      throw .invalid("Expected list field to have exactly one child")
+    }
+    let childType = try findArrowType(childField)
+    guard let name = childField.name else {
+      throw .invalid("Could not get name of child field")
+    }
+    let arrowField = ArrowField(
+      name: name,
+      dataType: childType,
+      isNullable: childField.nullable
+    )
+    return .list(arrowField)
+  default:
+    throw .invalid("Unhandled field type: \(field.typeType)")
+  }
+}
+
+func validateBufferIndex(_ recordBatch: FlatRecordBatch, index: Int32) throws {
+  if index >= recordBatch.buffersCount {
+    throw ArrowError.outOfBounds(index: Int64(index))
+  }
+}

From 4c4e54bd394491b9fb1c9a489a52771ceb154471 Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Sat, 1 Nov 2025 14:18:01 +0800
Subject: [PATCH 3/6] Rename ArrowArrayHolderBuilder to reflect change from
 ArrowArrayHolder to AnyArrowArray

---
 Sources/Arrow/ArrowArray.swift           |  2 -
 Sources/Arrow/ArrowArrayBuilder.swift    | 65 +++++++++++++-----------
 Sources/Arrow/ArrowArrayLoader.swift     |  1 +
 Sources/Arrow/ArrowEncoder.swift         | 15 +++---
 Sources/Arrow/ArrowReader.swift          |  2 +-
 Sources/Arrow/ArrowReaderHelper.swift    |  2 -
 Tests/ArrowTests/ArrayBuilderTests.swift | 56 ++++++++++----------
 Tests/ArrowTests/ArrayTests.swift        |  8 +--
 Tests/ArrowTests/CodableTests.swift      | 45 ++++++++--------
 Tests/ArrowTests/IPCTests.swift          | 12 ++---
 10 files changed, 106 insertions(+), 102 deletions(-)

diff --git a/Sources/Arrow/ArrowArray.swift b/Sources/Arrow/ArrowArray.swift
index 0405e85..9e47915 100644
--- a/Sources/Arrow/ArrowArray.swift
+++ b/Sources/Arrow/ArrowArray.swift
@@ -38,9 +38,7 @@ public protocol ArrowArray<ItemType>: AnyArrowArray {
 }
 
 // MARK: - Default Implementations
-
 extension ArrowArray {
-
   public var nullCount: UInt {
     arrowData.nullCount
   }
diff --git a/Sources/Arrow/ArrowArrayBuilder.swift b/Sources/Arrow/ArrowArrayBuilder.swift
index dae440f..ad50329 100644
--- a/Sources/Arrow/ArrowArrayBuilder.swift
+++ b/Sources/Arrow/ArrowArrayBuilder.swift
@@ -15,17 +15,15 @@
 
 import Foundation
 
-// FIXME: Rename or remove
-public protocol ArrowArrayHolderBuilder {
-  func toHolder() throws(ArrowError) -> AnyArrowArray
+public protocol AnyArrowArrayBuilder {
+  func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray
   func appendAny(_ val: Any?)
 }
 
 public class ArrowArrayBuilder<
-  T: ArrowBufferBuilder, U: ArrowArray<T.ItemType>
->:
-  ArrowArrayHolderBuilder
-{
+  T: ArrowBufferBuilder,
+  U: ArrowArray<T.ItemType>
+>: AnyArrowArrayBuilder {
   let type: ArrowType
   let bufferBuilder: T
   public var length: UInt { self.bufferBuilder.length }
@@ -73,13 +71,14 @@ public class ArrowArrayBuilder<
     self.type.getStride()
   }
 
-  public func toHolder() throws(ArrowError) -> AnyArrowArray {
+  public func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray {
     try self.finish()
   }
 }
 
 public class NumberArrayBuilder<T>: ArrowArrayBuilder<
-  FixedBufferBuilder<T>, FixedArray<T>
+  FixedBufferBuilder<T>,
+FixedArray<T>
 >
 where T: Numeric, T: BitwiseCopyable {
   fileprivate convenience init() throws(ArrowError) {
@@ -88,7 +87,8 @@ where T: Numeric, T: BitwiseCopyable {
 }
 
 public class StringArrayBuilder: ArrowArrayBuilder<
-  VariableBufferBuilder<String>, StringArray
+  VariableBufferBuilder<String>,
+  StringArray
 >
 {
   fileprivate convenience init() throws(ArrowError) {
@@ -97,7 +97,8 @@ public class StringArrayBuilder: ArrowArrayBuilder<
 }
 
 public class BinaryArrayBuilder: ArrowArrayBuilder<
-  VariableBufferBuilder<Data>, BinaryArray
+  VariableBufferBuilder<Data>,
+  BinaryArray
 >
 {
   fileprivate convenience init() throws(ArrowError) {
@@ -112,7 +113,8 @@ public class BoolArrayBuilder: ArrowArrayBuilder<BoolBufferBuilder, BoolArray> {
 }
 
 public class Date32ArrayBuilder: ArrowArrayBuilder<
-  Date32BufferBuilder, Date32Array
+  Date32BufferBuilder,
+  Date32Array
 >
 {
   fileprivate convenience init() throws(ArrowError) {
@@ -121,7 +123,8 @@ public class Date32ArrayBuilder: ArrowArrayBuilder<
 }
 
 public class Date64ArrayBuilder: ArrowArrayBuilder<
-  Date64BufferBuilder, Date64Array
+  Date64BufferBuilder,
+  Date64Array
 >
 {
   fileprivate convenience init() throws(ArrowError) {
@@ -130,7 +133,8 @@ public class Date64ArrayBuilder: ArrowArrayBuilder<
 }
 
 public class Time32ArrayBuilder: ArrowArrayBuilder<
-  FixedBufferBuilder<Time32>, Time32Array
+  FixedBufferBuilder<Time32>,
+  Time32Array
 >
 {
   fileprivate convenience init(_ unit: TimeUnit) throws(ArrowError) {
@@ -139,7 +143,8 @@ public class Time32ArrayBuilder: ArrowArrayBuilder<
 }
 
 public class Time64ArrayBuilder: ArrowArrayBuilder<
-  FixedBufferBuilder<Time64>, Time64Array
+  FixedBufferBuilder<Time64>,
+  Time64Array
 >
 {
   fileprivate convenience init(_ unit: TimeUnit) throws(ArrowError) {
@@ -148,7 +153,8 @@ public class Time64ArrayBuilder: ArrowArrayBuilder<
 }
 
 public class TimestampArrayBuilder: ArrowArrayBuilder<
-  FixedBufferBuilder<Int64>, TimestampArray
+  FixedBufferBuilder<Int64>,
+  TimestampArray
 >
 {
   fileprivate convenience init(
@@ -159,12 +165,13 @@ public class TimestampArrayBuilder: ArrowArrayBuilder<
 }
 
 public class StructArrayBuilder: ArrowArrayBuilder<
-  StructBufferBuilder, NestedArray
+  StructBufferBuilder,
+NestedArray
 >
 {
-  let builders: [any ArrowArrayHolderBuilder]
+  let builders: [any AnyArrowArrayBuilder]
   let fields: [ArrowField]
-  public init(_ fields: [ArrowField], builders: [any ArrowArrayHolderBuilder])
+  public init(_ fields: [ArrowField], builders: [any AnyArrowArrayBuilder])
     throws(ArrowError)
   {
     self.fields = fields
@@ -175,7 +182,7 @@ public class StructArrayBuilder: ArrowArrayBuilder<
 
   public init(_ fields: [ArrowField]) throws(ArrowError) {
     self.fields = fields
-    var builders: [any ArrowArrayHolderBuilder] = []
+    var builders: [any AnyArrowArrayBuilder] = []
     for field in fields {
       builders.append(
         try ArrowArrayBuilders.loadBuilder(arrowType: field.type))
@@ -201,7 +208,7 @@ public class StructArrayBuilder: ArrowArrayBuilder<
     let buffers = self.bufferBuilder.finish()
     var childData: [ArrowData] = []
     for builder in self.builders {
-      childData.append(try builder.toHolder().arrowData)
+      childData.append(try builder.toAnyArrowArray().arrowData)
     }
     let arrowData = ArrowData(
       self.type, buffers: buffers,
@@ -215,7 +222,7 @@ public class StructArrayBuilder: ArrowArrayBuilder<
 
 public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
 {
-  let valueBuilder: any ArrowArrayHolderBuilder
+  let valueBuilder: any AnyArrowArrayBuilder
 
   public override init(_ elementType: ArrowType) throws(ArrowError) {
 
@@ -240,7 +247,7 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
 
   public override func finish() throws(ArrowError) -> any ArrowArray<[Any?]> {
     let buffers = self.bufferBuilder.finish()
-    let childData = try valueBuilder.toHolder().arrowData
+    let childData = try valueBuilder.toAnyArrowArray().arrowData
     let arrowData = ArrowData(
       self.type,
       buffers: buffers,
@@ -252,10 +259,10 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
   }
 }
 
-public class ArrowArrayBuilders {
-  public static func loadBuilder(
-    _ builderType: Any.Type
-  ) throws(ArrowError) -> ArrowArrayHolderBuilder {
+public enum ArrowArrayBuilders {
+  public static func builder(
+    for builderType: Any.Type
+  ) throws(ArrowError) -> AnyArrowArrayBuilder {
     if builderType == Int8.self || builderType == Int8?.self {
       return try ArrowArrayBuilders.loadNumberArrayBuilder()
         as NumberArrayBuilder<Int8>
@@ -317,7 +324,7 @@ public class ArrowArrayBuilders {
     _ obj: T
   ) throws -> StructArrayBuilder {
     let mirror = Mirror(reflecting: obj)
-    var builders: [ArrowArrayHolderBuilder] = []
+    var builders: [AnyArrowArrayBuilder] = []
     var fields: [ArrowField] = []
     for (property, value) in mirror.children {
       guard let propertyName = property else {
@@ -339,7 +346,7 @@ public class ArrowArrayBuilders {
 
   public static func loadBuilder(
     arrowType: ArrowType
-  ) throws(ArrowError) -> ArrowArrayHolderBuilder {
+  ) throws(ArrowError) -> AnyArrowArrayBuilder {
     switch arrowType {
     case .uint8:
       return try loadNumberArrayBuilder() as NumberArrayBuilder<UInt8>
diff --git a/Sources/Arrow/ArrowArrayLoader.swift b/Sources/Arrow/ArrowArrayLoader.swift
index 56dbf43..b3b799b 100644
--- a/Sources/Arrow/ArrowArrayLoader.swift
+++ b/Sources/Arrow/ArrowArrayLoader.swift
@@ -13,6 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// TODO: Duplicated
 struct ArrowArrayLoader {
   public static func loadArray(
     _ arrowType: ArrowType,
diff --git a/Sources/Arrow/ArrowEncoder.swift b/Sources/Arrow/ArrowEncoder.swift
index a935891..f15573d 100644
--- a/Sources/Arrow/ArrowEncoder.swift
+++ b/Sources/Arrow/ArrowEncoder.swift
@@ -15,7 +15,7 @@
 import Foundation
 
 public class ArrowEncoder: Encoder {
-  public private(set) var builders: [String: ArrowArrayHolderBuilder] = [:]
+  public private(set) var builders: [String: AnyArrowArrayBuilder] = [:]
   private var byIndex: [String] = []
   public var codingPath: [CodingKey] = []
   public var userInfo: [CodingUserInfoKey: Any] = [:]
@@ -29,9 +29,7 @@ public class ArrowEncoder: Encoder {
 
   public init() {}
 
-  public init(
-    _ builders: [String: ArrowArrayHolderBuilder], byIndex: [String]
-  ) {
+  public init(_ builders: [String: AnyArrowArrayBuilder], byIndex: [String]) {
     self.builders = builders
     self.byIndex = byIndex
   }
@@ -59,14 +57,13 @@ public class ArrowEncoder: Encoder {
     // this will check if T is a simple built in type
     // (UInt, Int, Int8, String, Date, etc...).
     if ArrowArrayBuilders.isValidBuilderType(T.self) {
-      let builders = ["col0": try ArrowArrayBuilders.loadBuilder(T.self)]
+      let builders = ["col0": try ArrowArrayBuilders.builder(for: T.self)]
       return ArrowEncoder(builders, byIndex: ["col0"])
     } else {
       let encoder = ArrowEncoder()
       if data is [AnyHashable: Any] {
         encoder.modForIndex = 2
       }
-
       return encoder
     }
   }
@@ -78,7 +75,7 @@ public class ArrowEncoder: Encoder {
       guard let builder = builders[key] else {
         throw .invalid("Missing builder for \(key)")
       }
-      batchBuilder.addColumn(key, arrowArray: try builder.toHolder())
+      batchBuilder.addColumn(key, arrowArray: try builder.toAnyArrowArray())
     }
     return try batchBuilder.finish().get()
   }
@@ -116,12 +113,12 @@ public class ArrowEncoder: Encoder {
   func ensureColumnExists<T>(
     _ value: T,
     key: String
-  ) throws(ArrowError) -> ArrowArrayHolderBuilder {
+  ) throws(ArrowError) -> AnyArrowArrayBuilder {
     try throwIfInvalid()
     if let builder = builders[key] {
       return builder
     }
-    let builder = try ArrowArrayBuilders.loadBuilder(T.self)
+    let builder = try ArrowArrayBuilders.builder(for: T.self)
     builders[key] = builder
     byIndex.append(key)
     return builder
diff --git a/Sources/Arrow/ArrowReader.swift b/Sources/Arrow/ArrowReader.swift
index 006c165..f3985b1 100644
--- a/Sources/Arrow/ArrowReader.swift
+++ b/Sources/Arrow/ArrowReader.swift
@@ -544,7 +544,7 @@ public struct ArrowReader: Sendable {
         .unknownError("Unhandled header type: \(message.headerType)"))
     }
   }
-  
+
   func validateFileData(_ data: Data) -> Bool {
     let markerLength = fileMarker.count
     let startString = data[..<markerLength]
diff --git a/Sources/Arrow/ArrowReaderHelper.swift b/Sources/Arrow/ArrowReaderHelper.swift
index 08cd49e..97cfccd 100644
--- a/Sources/Arrow/ArrowReaderHelper.swift
+++ b/Sources/Arrow/ArrowReaderHelper.swift
@@ -217,8 +217,6 @@ func makeArrayHolder(
   }
 }
 
-
-
 func getUInt32(_ data: Data, offset: Int) -> UInt32 {
   let token = data.withUnsafeBytes { rawBuffer in
     rawBuffer.loadUnaligned(fromByteOffset: offset, as: UInt32.self)
diff --git a/Tests/ArrowTests/ArrayBuilderTests.swift b/Tests/ArrowTests/ArrayBuilderTests.swift
index 4a648c4..c7555f6 100644
--- a/Tests/ArrowTests/ArrayBuilderTests.swift
+++ b/Tests/ArrowTests/ArrayBuilderTests.swift
@@ -53,36 +53,36 @@ struct ArrayBuilderTests {
 
   @Test func loadArrayBuilders() throws {
     #expect(throws: Never.self) {
-      let _ = try ArrowArrayBuilders.loadBuilder(Int8.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int16.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int32.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int64.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt8.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt16.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt32.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt64.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Float.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Double.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Date.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Bool.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int8?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int16?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int32?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int64?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt8?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt16?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt32?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt64?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Float?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Double?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Date?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Bool?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int8.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int16.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int32.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int64.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt8.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt16.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt32.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt64.self)
+      let _ = try ArrowArrayBuilders.builder(for: Float.self)
+      let _ = try ArrowArrayBuilders.builder(for: Double.self)
+      let _ = try ArrowArrayBuilders.builder(for: Date.self)
+      let _ = try ArrowArrayBuilders.builder(for: Bool.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int8?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int16?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int32?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int64?.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt8?.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt16?.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt32?.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt64?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Float?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Double?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Date?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Bool?.self)
     }
     #expect(throws: ArrowError.self) {
-      let _ = try ArrowArrayBuilders.loadBuilder(Int.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(Int?.self)
-      let _ = try ArrowArrayBuilders.loadBuilder(UInt?.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt.self)
+      let _ = try ArrowArrayBuilders.builder(for: Int?.self)
+      let _ = try ArrowArrayBuilders.builder(for: UInt?.self)
     }
   }
 }
diff --git a/Tests/ArrowTests/ArrayTests.swift b/Tests/ArrowTests/ArrayTests.swift
index 553bec1..ef40a22 100644
--- a/Tests/ArrowTests/ArrayTests.swift
+++ b/Tests/ArrowTests/ArrayTests.swift
@@ -452,18 +452,18 @@ struct ArrayTests {
   }
 
   @Test func arrowArrayHolderBuilder() throws {
-    let uint8HBuilder: ArrowArrayHolderBuilder =
+    let uint8HBuilder: AnyArrowArrayBuilder =
       (try ArrowArrayBuilders.loadNumberArrayBuilder()
         as NumberArrayBuilder<UInt8>)
     for index in 0..<100 {
       uint8HBuilder.appendAny(UInt8(index))
     }
 
-    let uint8Holder = try uint8HBuilder.toHolder()
+    let uint8Holder = try uint8HBuilder.toAnyArrowArray()
     #expect(uint8Holder.nullCount == 0)
     #expect(uint8Holder.length == 100)
 
-    let stringHBuilder: ArrowArrayHolderBuilder =
+    let stringHBuilder: AnyArrowArrayBuilder =
       (try ArrowArrayBuilders.loadStringArrayBuilder())
     for index in 0..<100 {
       if index % 10 == 9 {
@@ -473,7 +473,7 @@ struct ArrayTests {
       }
     }
 
-    let stringHolder = try stringHBuilder.toHolder()
+    let stringHolder = try stringHBuilder.toAnyArrowArray()
     #expect(stringHolder.nullCount == 10)
     #expect(stringHolder.length == 100)
   }
diff --git a/Tests/ArrowTests/CodableTests.swift b/Tests/ArrowTests/CodableTests.swift
index 67ae61d..8ae2f0f 100644
--- a/Tests/ArrowTests/CodableTests.swift
+++ b/Tests/ArrowTests/CodableTests.swift
@@ -91,19 +91,19 @@ struct CodableTests {
     stringBuilder.append("test0", "test1", "test2")
     dateBuilder.append(date1, date1, date1)
     let result = RecordBatch.Builder()
-      .addColumn("propBool", arrowArray: try boolBuilder.toHolder())
-      .addColumn("propInt8", arrowArray: try int8Builder.toHolder())
-      .addColumn("propInt16", arrowArray: try int16Builder.toHolder())
-      .addColumn("propInt32", arrowArray: try int32Builder.toHolder())
-      .addColumn("propInt64", arrowArray: try int64Builder.toHolder())
-      .addColumn("propUInt8", arrowArray: try uint8Builder.toHolder())
-      .addColumn("propUInt16", arrowArray: try uint16Builder.toHolder())
-      .addColumn("propUInt32", arrowArray: try uint32Builder.toHolder())
-      .addColumn("propUInt64", arrowArray: try uint64Builder.toHolder())
-      .addColumn("propFloat", arrowArray: try floatBuilder.toHolder())
-      .addColumn("propDouble", arrowArray: try doubleBuilder.toHolder())
-      .addColumn("propString", arrowArray: try stringBuilder.toHolder())
-      .addColumn("propDate", arrowArray: try dateBuilder.toHolder())
+      .addColumn("propBool", arrowArray: try boolBuilder.finish())
+      .addColumn("propInt8", arrowArray: try int8Builder.finish())
+      .addColumn("propInt16", arrowArray: try int16Builder.finish())
+      .addColumn("propInt32", arrowArray: try int32Builder.finish())
+      .addColumn("propInt64", arrowArray: try int64Builder.finish())
+      .addColumn("propUInt8", arrowArray: try uint8Builder.finish())
+      .addColumn("propUInt16", arrowArray: try uint16Builder.finish())
+      .addColumn("propUInt32", arrowArray: try uint32Builder.finish())
+      .addColumn("propUInt64", arrowArray: try uint64Builder.finish())
+      .addColumn("propFloat", arrowArray: try floatBuilder.finish())
+      .addColumn("propDouble", arrowArray: try doubleBuilder.finish())
+      .addColumn("propString", arrowArray: try stringBuilder.finish())
+      .addColumn("propDate", arrowArray: try dateBuilder.finish())
       .finish()
     switch result {
     case .success(let rb):
@@ -139,7 +139,7 @@ struct CodableTests {
       try ArrowArrayBuilders.loadNumberArrayBuilder()
     int8Builder.append(10, 11, 12)
     let result = RecordBatch.Builder()
-      .addColumn("propInt8", arrowArray: try int8Builder.toHolder())
+      .addColumn("propInt8", arrowArray: try int8Builder.finish())
       .finish()
     switch result {
     case .success(let rb):
@@ -159,7 +159,10 @@ struct CodableTests {
       try ArrowArrayBuilders.loadNumberArrayBuilder()
     int8WNilBuilder.append(10, nil, 12, nil)
     let resultWNil = RecordBatch.Builder()
-      .addColumn("propInt8", arrowArray: try int8WNilBuilder.toHolder())
+      .addColumn(
+        "propInt8",
+        arrowArray: try int8WNilBuilder.finish()
+      )
       .finish()
     switch resultWNil {
     case .success(let rb):
@@ -185,8 +188,8 @@ struct CodableTests {
     int8Builder.append(10, 11, 12, 13)
     stringBuilder.append("test10", "test11", "test12", "test13")
     switch RecordBatch.Builder()
-      .addColumn("propInt8", arrowArray: try int8Builder.toHolder())
-      .addColumn("propString", arrowArray: try stringBuilder.toHolder())
+      .addColumn("propInt8", arrowArray: try int8Builder.finish())
+      .addColumn("propString", arrowArray: try stringBuilder.finish())
       .finish()
     {
     case .success(let rb):
@@ -200,8 +203,8 @@ struct CodableTests {
     }
 
     switch RecordBatch.Builder()
-      .addColumn("propString", arrowArray: try stringBuilder.toHolder())
-      .addColumn("propInt8", arrowArray: try int8Builder.toHolder())
+      .addColumn("propString", arrowArray: try stringBuilder.finish())
+      .addColumn("propInt8", arrowArray: try int8Builder.finish())
       .finish()
     {
     case .success(let rb):
@@ -222,8 +225,8 @@ struct CodableTests {
     int8Builder.append(10, 11, 12, 13)
     stringWNilBuilder.append(nil, "test11", nil, "test13")
     let resultWNil = RecordBatch.Builder()
-      .addColumn("propInt8", arrowArray: try int8Builder.toHolder())
-      .addColumn("propString", arrowArray: try stringWNilBuilder.toHolder())
+      .addColumn("propInt8", arrowArray: try int8Builder.finish())
+      .addColumn("propString", arrowArray: try stringWNilBuilder.finish())
       .finish()
     switch resultWNil {
     case .success(let rb):
diff --git a/Tests/ArrowTests/IPCTests.swift b/Tests/ArrowTests/IPCTests.swift
index 83abf3a..f8ded1a 100644
--- a/Tests/ArrowTests/IPCTests.swift
+++ b/Tests/ArrowTests/IPCTests.swift
@@ -71,9 +71,9 @@ func checkBoolRecordBatch(
     #expect(recordBatch.schema.fields[1].type == .utf8)
     for index in 0..<recordBatch.length {
       let column = recordBatch.columns[0]
-//      guard let str = column as? AsString else {
-//        throw .invalid("Could not cast column to AsString")
-//      }
+      //      guard let str = column as? AsString else {
+      //        throw .invalid("Could not cast column to AsString")
+      //      }
       let val = "\(column.asString(index))"
       if index == 0 || index == 4 {
         #expect(val == "true")
@@ -118,9 +118,9 @@ func checkStructRecordBatch(
     #expect(fields[0].type == .utf8)
     #expect(fields[1].type == .boolean)
     let column = recordBatch.columns[0]
-//    guard let str = column else {
-//      throw .runtimeError("String array is nil")
-//    }
+    //    guard let str = column else {
+    //      throw .runtimeError("String array is nil")
+    //    }
     #expect("\(column.asString(0))" == "{0,false}")
     #expect("\(column.asString(1))" == "{1,true}")
     #expect(column.asAny(2) == nil)

From d98aaf9d17c7fab47bbe260cc50f09612e5f892b Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Sat, 1 Nov 2025 15:59:00 +0800
Subject: [PATCH 4/6] Clearly name the type parameters on ArrowArrayBuilder.

---
 Sources/Arrow/ArrowArrayBuilder.swift | 38 ++++++++++++++-------------
 Sources/Arrow/ArrowTable.swift        |  7 +++++
 2 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/Sources/Arrow/ArrowArrayBuilder.swift b/Sources/Arrow/ArrowArrayBuilder.swift
index ad50329..280604f 100644
--- a/Sources/Arrow/ArrowArrayBuilder.swift
+++ b/Sources/Arrow/ArrowArrayBuilder.swift
@@ -21,54 +21,56 @@ public protocol AnyArrowArrayBuilder {
 }
 
 public class ArrowArrayBuilder<
-  T: ArrowBufferBuilder,
-  U: ArrowArray<T.ItemType>
+  BufferBuilder: ArrowBufferBuilder,
+  ArrayType: ArrowArray<BufferBuilder.ItemType>
 >: AnyArrowArrayBuilder {
-  let type: ArrowType
-  let bufferBuilder: T
+  let arrowType: ArrowType
+  let bufferBuilder: BufferBuilder
   public var length: UInt { self.bufferBuilder.length }
   public var capacity: UInt { self.bufferBuilder.capacity }
   public var nullCount: UInt { self.bufferBuilder.nullCount }
   public var offset: UInt { self.bufferBuilder.offset }
 
   fileprivate init(_ type: ArrowType) throws(ArrowError) {
-    self.type = type
-    self.bufferBuilder = T()
+    self.arrowType = type
+    self.bufferBuilder = BufferBuilder()
   }
 
-  public func append(_ vals: T.ItemType?...) {
+  public func append(_ vals: BufferBuilder.ItemType?...) {
     for val in vals {
       self.bufferBuilder.append(val)
     }
   }
 
-  public func append(_ vals: [T.ItemType?]) {
+  public func append(_ vals: [BufferBuilder.ItemType?]) {
     for val in vals {
       self.bufferBuilder.append(val)
     }
   }
 
-  public func append(_ val: T.ItemType?) {
+  public func append(_ val: BufferBuilder.ItemType?) {
     self.bufferBuilder.append(val)
   }
 
   public func appendAny(_ val: Any?) {
-    self.bufferBuilder.append(val as? T.ItemType)
+    self.bufferBuilder.append(val as? BufferBuilder.ItemType)
   }
 
-  public func finish() throws(ArrowError) -> any ArrowArray<T.ItemType> {
+  public func finish() throws(ArrowError) -> any ArrowArray<
+    BufferBuilder.ItemType
+  > {
     let buffers = self.bufferBuilder.finish()
     let arrowData = ArrowData(
-      self.type,
+      self.arrowType,
       buffers: buffers,
       nullCount: self.nullCount
     )
-    let array = try U(arrowData)
+    let array = try ArrayType(arrowData)
     return array
   }
 
   public func getStride() -> Int {
-    self.type.getStride()
+    self.arrowType.getStride()
   }
 
   public func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray {
@@ -78,7 +80,7 @@ public class ArrowArrayBuilder<
 
 public class NumberArrayBuilder<T>: ArrowArrayBuilder<
   FixedBufferBuilder<T>,
-FixedArray<T>
+  FixedArray<T>
 >
 where T: Numeric, T: BitwiseCopyable {
   fileprivate convenience init() throws(ArrowError) {
@@ -166,7 +168,7 @@ public class TimestampArrayBuilder: ArrowArrayBuilder<
 
 public class StructArrayBuilder: ArrowArrayBuilder<
   StructBufferBuilder,
-NestedArray
+  NestedArray
 >
 {
   let builders: [any AnyArrowArrayBuilder]
@@ -211,7 +213,7 @@ NestedArray
       childData.append(try builder.toAnyArrowArray().arrowData)
     }
     let arrowData = ArrowData(
-      self.type, buffers: buffers,
+      self.arrowType, buffers: buffers,
       children: childData,
       nullCount: self.nullCount,
       length: self.length)
@@ -249,7 +251,7 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
     let buffers = self.bufferBuilder.finish()
     let childData = try valueBuilder.toAnyArrowArray().arrowData
     let arrowData = ArrowData(
-      self.type,
+      self.arrowType,
       buffers: buffers,
       children: [childData],
       nullCount: self.nullCount,
diff --git a/Sources/Arrow/ArrowTable.swift b/Sources/Arrow/ArrowTable.swift
index fdfcba4..d1daebd 100644
--- a/Sources/Arrow/ArrowTable.swift
+++ b/Sources/Arrow/ArrowTable.swift
@@ -210,6 +210,7 @@ public class RecordBatch {
   public var columnCount: UInt { UInt(self.columns.count) }
   public let columns: [AnyArrowArray]
   public let length: UInt
+
   public init(_ schema: ArrowSchema, columns: [AnyArrowArray]) {
     self.schema = schema
     self.columns = columns
@@ -222,6 +223,12 @@ public class RecordBatch {
 
     public init() {}
 
+    /// Add a column the `RecordBatch` builder.
+    /// - Parameters:
+    ///   - fieldName: The field name.
+    ///   - arrowArray: The array to add to the reocrd batch.
+    /// - Returns: The `RecordBatch.Builder` with the array appended and the field added to
+    /// the schema. If the array contains zero nulls, the field is defined as non-null.
     @discardableResult
     public func addColumn(
       _ fieldName: String,

From 604a822a9c0ef9abcb36653e44593d03d5bc6824 Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Sat, 1 Nov 2025 16:16:32 +0800
Subject: [PATCH 5/6] Introduce  ArrowArrayBuilderProtocol which will become
 the ArrowArrayBuilder base.

---
 Sources/Arrow/ArrowArrayBuilder.swift | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/Sources/Arrow/ArrowArrayBuilder.swift b/Sources/Arrow/ArrowArrayBuilder.swift
index 280604f..4372a94 100644
--- a/Sources/Arrow/ArrowArrayBuilder.swift
+++ b/Sources/Arrow/ArrowArrayBuilder.swift
@@ -1,5 +1,5 @@
 // Copyright 2025 The Apache Software Foundation
-// Copyright 2025 The Columnar-Swift Contributors
+// Copyright 2025 The Columnar Swift Contributors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -20,10 +20,20 @@ public protocol AnyArrowArrayBuilder {
   func appendAny(_ val: Any?)
 }
 
+/// A type which can build an `ArrowArray`of `ItemType`.
+public protocol ArrowArrayBuilderProtocol {
+  associatedtype BufferBuilder: ArrowBufferBuilder
+  associatedtype ArrayType: ArrowArray
+  where ArrayType.ItemType == BufferBuilder.ItemType
+
+  mutating func append(_ value: BufferBuilder.ItemType?) throws(ArrowError)
+  func finish() throws(ArrowError) -> ArrayType
+}
+
 public class ArrowArrayBuilder<
   BufferBuilder: ArrowBufferBuilder,
   ArrayType: ArrowArray<BufferBuilder.ItemType>
->: AnyArrowArrayBuilder {
+>: AnyArrowArrayBuilder, ArrowArrayBuilderProtocol {
   let arrowType: ArrowType
   let bufferBuilder: BufferBuilder
   public var length: UInt { self.bufferBuilder.length }
@@ -56,9 +66,7 @@ public class ArrowArrayBuilder<
     self.bufferBuilder.append(val as? BufferBuilder.ItemType)
   }
 
-  public func finish() throws(ArrowError) -> any ArrowArray<
-    BufferBuilder.ItemType
-  > {
+  public func finish() throws(ArrowError) -> ArrayType {
     let buffers = self.bufferBuilder.finish()
     let arrowData = ArrowData(
       self.arrowType,
@@ -206,7 +214,7 @@ public class StructArrayBuilder: ArrowArrayBuilder<
     }
   }
 
-  public override func finish() throws(ArrowError) -> any ArrowArray<[Any?]> {
+  public override func finish() throws(ArrowError) -> ArrayType {
     let buffers = self.bufferBuilder.finish()
     var childData: [ArrowData] = []
     for builder in self.builders {
@@ -247,7 +255,7 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
     }
   }
 
-  public override func finish() throws(ArrowError) -> any ArrowArray<[Any?]> {
+  public override func finish() throws(ArrowError) -> ArrayType {
     let buffers = self.bufferBuilder.finish()
     let childData = try valueBuilder.toAnyArrowArray().arrowData
     let arrowData = ArrowData(

From ee6e143e55d86bbdc8e257c8554e527908ea2d2b Mon Sep 17 00:00:00 2001
From: Will Temperley <willtemperley@gmail.com>
Date: Sat, 1 Nov 2025 20:51:51 +0800
Subject: [PATCH 6/6] Migrate most ArrowArrayBuilder functions to protocol
 extensions.

---
 Sources/Arrow/ArrowArrayBuilder.swift | 127 +++++++++++++++++---------
 Tests/ArrowTests/ArrayTests.swift     |   2 +-
 Tests/ArrowTests/IPCTests.swift       |   2 +-
 3 files changed, 84 insertions(+), 47 deletions(-)

diff --git a/Sources/Arrow/ArrowArrayBuilder.swift b/Sources/Arrow/ArrowArrayBuilder.swift
index 4372a94..e7ef607 100644
--- a/Sources/Arrow/ArrowArrayBuilder.swift
+++ b/Sources/Arrow/ArrowArrayBuilder.swift
@@ -15,36 +15,38 @@
 
 import Foundation
 
+// MARK: Array builder interface.
+
+/// A type which builds a type-erased `ArrowArray`.
 public protocol AnyArrowArrayBuilder {
   func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray
   func appendAny(_ val: Any?)
 }
 
 /// A type which can build an `ArrowArray`of `ItemType`.
-public protocol ArrowArrayBuilderProtocol {
+public protocol ArrowArrayBuilder {
   associatedtype BufferBuilder: ArrowBufferBuilder
   associatedtype ArrayType: ArrowArray
   where ArrayType.ItemType == BufferBuilder.ItemType
 
-  mutating func append(_ value: BufferBuilder.ItemType?) throws(ArrowError)
+  func append(_ vals: BufferBuilder.ItemType?...)
+  func append(_ vals: [BufferBuilder.ItemType?])
+  func append(_ val: BufferBuilder.ItemType?)
+  func appendAny(_ val: Any?)
   func finish() throws(ArrowError) -> ArrayType
 }
 
-public class ArrowArrayBuilder<
-  BufferBuilder: ArrowBufferBuilder,
-  ArrayType: ArrowArray<BufferBuilder.ItemType>
->: AnyArrowArrayBuilder, ArrowArrayBuilderProtocol {
-  let arrowType: ArrowType
-  let bufferBuilder: BufferBuilder
-  public var length: UInt { self.bufferBuilder.length }
-  public var capacity: UInt { self.bufferBuilder.capacity }
-  public var nullCount: UInt { self.bufferBuilder.nullCount }
-  public var offset: UInt { self.bufferBuilder.offset }
+internal protocol ArrowArrayBuilderInternal: ArrowArrayBuilder {
+  var arrowType: ArrowType { get }
+  var bufferBuilder: BufferBuilder { get }
+}
 
-  fileprivate init(_ type: ArrowType) throws(ArrowError) {
-    self.arrowType = type
-    self.bufferBuilder = BufferBuilder()
-  }
+extension ArrowArrayBuilderInternal {
+
+  var length: UInt { self.bufferBuilder.length }
+  var capacity: UInt { self.bufferBuilder.capacity }
+  var nullCount: UInt { self.bufferBuilder.nullCount }
+  var offset: UInt { self.bufferBuilder.offset }
 
   public func append(_ vals: BufferBuilder.ItemType?...) {
     for val in vals {
@@ -66,6 +68,35 @@ public class ArrowArrayBuilder<
     self.bufferBuilder.append(val as? BufferBuilder.ItemType)
   }
 
+  /// Returns the byte width of this type if it is a primitive type.
+  public func stride() -> Int {
+    self.arrowType.getStride()
+  }
+
+  /// Returns an unparameterised `ArrowArray`.
+  /// - Returns: The type-erased Arrow array.
+  public func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray {
+    try self.finish()
+  }
+}
+
+// MARK: Base implementation.
+
+// Note: It would be preferable to move all of this to a protocol, however
+// ListArrayBuilder overrides finish. This is delicate because protocol
+// extension method dispatching means the
+public class ArrowArrayBuilderBase<
+  BufferBuilder: ArrowBufferBuilder,
+  ArrayType: ArrowArray<BufferBuilder.ItemType>
+>: AnyArrowArrayBuilder, ArrowArrayBuilderInternal {
+  let arrowType: ArrowType
+  let bufferBuilder: BufferBuilder
+
+  fileprivate init(_ type: ArrowType) throws(ArrowError) {
+    self.arrowType = type
+    self.bufferBuilder = BufferBuilder()
+  }
+
   public func finish() throws(ArrowError) -> ArrayType {
     let buffers = self.bufferBuilder.finish()
     let arrowData = ArrowData(
@@ -76,27 +107,20 @@ public class ArrowArrayBuilder<
     let array = try ArrayType(arrowData)
     return array
   }
-
-  public func getStride() -> Int {
-    self.arrowType.getStride()
-  }
-
-  public func toAnyArrowArray() throws(ArrowError) -> AnyArrowArray {
-    try self.finish()
-  }
 }
 
-public class NumberArrayBuilder<T>: ArrowArrayBuilder<
-  FixedBufferBuilder<T>,
-  FixedArray<T>
+/// A type which builds an `ArrowArray` with a numeric `ItemType`.
+public class NumberArrayBuilder<ItemType>: ArrowArrayBuilderBase<
+  FixedBufferBuilder<ItemType>,
+  FixedArray<ItemType>
 >
-where T: Numeric, T: BitwiseCopyable {
+where ItemType: Numeric, ItemType: BitwiseCopyable {
   fileprivate convenience init() throws(ArrowError) {
-    try self.init(try ArrowTypeConverter.infoForNumericType(T.self))
+    try self.init(try ArrowTypeConverter.infoForNumericType(ItemType.self))
   }
 }
 
-public class StringArrayBuilder: ArrowArrayBuilder<
+public class StringArrayBuilder: ArrowArrayBuilderBase<
   VariableBufferBuilder<String>,
   StringArray
 >
@@ -106,7 +130,7 @@ public class StringArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class BinaryArrayBuilder: ArrowArrayBuilder<
+public class BinaryArrayBuilder: ArrowArrayBuilderBase<
   VariableBufferBuilder<Data>,
   BinaryArray
 >
@@ -116,13 +140,16 @@ public class BinaryArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class BoolArrayBuilder: ArrowArrayBuilder<BoolBufferBuilder, BoolArray> {
+public class BoolArrayBuilder: ArrowArrayBuilderBase<
+  BoolBufferBuilder, BoolArray
+>
+{
   fileprivate convenience init() throws(ArrowError) {
     try self.init(.boolean)
   }
 }
 
-public class Date32ArrayBuilder: ArrowArrayBuilder<
+public class Date32ArrayBuilder: ArrowArrayBuilderBase<
   Date32BufferBuilder,
   Date32Array
 >
@@ -132,7 +159,7 @@ public class Date32ArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class Date64ArrayBuilder: ArrowArrayBuilder<
+public class Date64ArrayBuilder: ArrowArrayBuilderBase<
   Date64BufferBuilder,
   Date64Array
 >
@@ -142,7 +169,7 @@ public class Date64ArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class Time32ArrayBuilder: ArrowArrayBuilder<
+public class Time32ArrayBuilder: ArrowArrayBuilderBase<
   FixedBufferBuilder<Time32>,
   Time32Array
 >
@@ -152,7 +179,7 @@ public class Time32ArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class Time64ArrayBuilder: ArrowArrayBuilder<
+public class Time64ArrayBuilder: ArrowArrayBuilderBase<
   FixedBufferBuilder<Time64>,
   Time64Array
 >
@@ -162,7 +189,7 @@ public class Time64ArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class TimestampArrayBuilder: ArrowArrayBuilder<
+public class TimestampArrayBuilder: ArrowArrayBuilderBase<
   FixedBufferBuilder<Int64>,
   TimestampArray
 >
@@ -174,16 +201,19 @@ public class TimestampArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class StructArrayBuilder: ArrowArrayBuilder<
+// MARK: Struct array builder.
+
+public class StructArrayBuilder: ArrowArrayBuilderBase<
   StructBufferBuilder,
   NestedArray
 >
 {
   let builders: [any AnyArrowArrayBuilder]
   let fields: [ArrowField]
-  public init(_ fields: [ArrowField], builders: [any AnyArrowArrayBuilder])
-    throws(ArrowError)
-  {
+  public init(
+    _ fields: [ArrowField],
+    builders: [any AnyArrowArrayBuilder]
+  ) throws(ArrowError) {
     self.fields = fields
     self.builders = builders
     try super.init(.strct(fields))
@@ -201,7 +231,7 @@ public class StructArrayBuilder: ArrowArrayBuilder<
     try super.init(.strct(fields))
   }
 
-  public override func append(_ values: [Any?]?) {
+  public func append(_ values: [Any?]?) {
     self.bufferBuilder.append(values)
     if let anyValues = values {
       for index in 0..<builders.count {
@@ -230,7 +260,13 @@ public class StructArrayBuilder: ArrowArrayBuilder<
   }
 }
 
-public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
+// MARK: List array builder.
+
+/// A type which can build an `NestedArray`containing exactly `ItemType`.
+public class ListArrayBuilder: ArrowArrayBuilderBase<
+  ListBufferBuilder,
+  NestedArray
+>
 {
   let valueBuilder: any AnyArrowArrayBuilder
 
@@ -246,7 +282,8 @@ public class ListArrayBuilder: ArrowArrayBuilder<ListBufferBuilder, NestedArray>
     try super.init(elementType)
   }
 
-  public override func append(_ values: [Any?]?) {
+  // Overrides the default
+  public func append(_ values: [Any?]?) {
     self.bufferBuilder.append(values)
     if let vals = values {
       for val in vals {
@@ -330,7 +367,7 @@ public enum ArrowArrayBuilders {
       || type == Float.self || type == Date.self
   }
 
-  public static func loadStructArrayBuilderForType<T>(
+  public static func structArrayBuilderForType<T>(
     _ obj: T
   ) throws -> StructArrayBuilder {
     let mirror = Mirror(reflecting: obj)
diff --git a/Tests/ArrowTests/ArrayTests.swift b/Tests/ArrowTests/ArrayTests.swift
index ef40a22..4bf0755 100644
--- a/Tests/ArrowTests/ArrayTests.swift
+++ b/Tests/ArrowTests/ArrayTests.swift
@@ -361,7 +361,7 @@ struct ArrayTests {
 
     let testData = StructTest()
     let dateNow = Date.now
-    let structBuilder = try ArrowArrayBuilders.loadStructArrayBuilderForType(
+    let structBuilder = try ArrowArrayBuilders.structArrayBuilderForType(
       testData)
     structBuilder.append([
       true, Int8(1), Int16(2), Int32(3), Int64(4),
diff --git a/Tests/ArrowTests/IPCTests.swift b/Tests/ArrowTests/IPCTests.swift
index f8ded1a..8b0b9ea 100644
--- a/Tests/ArrowTests/IPCTests.swift
+++ b/Tests/ArrowTests/IPCTests.swift
@@ -168,7 +168,7 @@ func makeStructSchema() throws -> ArrowSchema {
 func makeStructRecordBatch() throws -> RecordBatch {
   let testData = StructTest()
   let dateNow = Date.now
-  let structBuilder = try ArrowArrayBuilders.loadStructArrayBuilderForType(
+  let structBuilder = try ArrowArrayBuilders.structArrayBuilderForType(
     testData
   )
   structBuilder.append([