chore: Suppress 'as' test is always true warning (#54)

## What's Changed

Remove needless `as ArrowError`s because all errors must be `ArrowError`
here.

Closes #52.

Author: kou

Arrow/Sources/Arrow/ArrowReader.swift

@@ -247,22 +247,21 @@ public class ArrowReader { // swiftlint:disable:this type_body_length
             let message = org_apache_arrow_flatbuf_Message.getRootAsMessage(bb: dataBuffer)
             switch message.headerType {
             case .recordbatch:
-                do {
-                    let rbMessage = message.header(type: org_apache_arrow_flatbuf_RecordBatch.self)!
-                    let recordBatch = try loadRecordBatch(
-                        rbMessage,
-                        schema: schemaMessage!,
-                        arrowSchema: result.schema!,
-                        data: input,
-                        messageEndOffset: (Int64(offset) + Int64(length))).get()
+                let rbMessage = message.header(type: org_apache_arrow_flatbuf_RecordBatch.self)!
+                let recordBatchResult = loadRecordBatch(
+                    rbMessage,
+                    schema: schemaMessage!,
+                    arrowSchema: result.schema!,
+                    data: input,
+                    messageEndOffset: (Int64(offset) + Int64(length)))
+                switch recordBatchResult {
+                case .success(let recordBatch):
                     result.batches.append(recordBatch)
-                    offset += Int(message.bodyLength + Int64(length))
-                    length = getUInt32(input, offset: offset)
-                } catch let error as ArrowError {
+                case .failure(let error):
                     return .failure(error)
-                } catch {
-                    return .failure(.unknownError("Unexpected error: \(error)"))
                 }
+                offset += Int(message.bodyLength + Int64(length))
+                length = getUInt32(input, offset: offset)
             case .schema:
                 schemaMessage = message.header(type: org_apache_arrow_flatbuf_Schema.self)!
                 let schemaResult = loadSchema(schemaMessage!)
@@ -334,19 +333,18 @@ public class ArrowReader { // swiftlint:disable:this type_body_length
             let message = org_apache_arrow_flatbuf_Message.getRootAsMessage(bb: mbb)
             switch message.headerType {
             case .recordbatch:
-                do {
-                    let rbMessage = message.header(type: org_apache_arrow_flatbuf_RecordBatch.self)!
-                    let recordBatch = try loadRecordBatch(
-                        rbMessage,
-                        schema: footer.schema!,
-                        arrowSchema: result.schema!,
-                        data: fileData,
-                        messageEndOffset: messageEndOffset).get()
+                let rbMessage = message.header(type: org_apache_arrow_flatbuf_RecordBatch.self)!
+                let recordBatchResult = loadRecordBatch(
+                    rbMessage,
+                    schema: footer.schema!,
+                    arrowSchema: result.schema!,
+                    data: fileData,
+                    messageEndOffset: messageEndOffset)
+                switch recordBatchResult {
+                case .success(let recordBatch):
                     result.batches.append(recordBatch)
-                } catch let error as ArrowError {
+                case .failure(let error):
                     return .failure(error)
-                } catch {
-                    return .failure(.unknownError("Unexpected error: \(error)"))
                 }
             default:
                 return .failure(.unknownError("Unhandled header type: \(message.headerType)"))
@@ -399,16 +397,15 @@ public class ArrowReader { // swiftlint:disable:this type_body_length
             }
         case .recordbatch:
             let rbMessage = message.header(type: org_apache_arrow_flatbuf_RecordBatch.self)!
-            do {
-                let recordBatch = try loadRecordBatch(
-                    rbMessage, schema: result.messageSchema!, arrowSchema: result.schema!,
-                    data: dataBody, messageEndOffset: 0).get()
+            let recordBatchResult = loadRecordBatch(
+                rbMessage, schema: result.messageSchema!, arrowSchema: result.schema!,
+                data: dataBody, messageEndOffset: 0)
+            switch recordBatchResult {
+            case .success(let recordBatch):
                 result.batches.append(recordBatch)
                 return .success(())
-            } catch let error as ArrowError {
+            case .failure(let error):
                 return .failure(error)
-            } catch {
-                return .failure(.unknownError("Unexpected error: \(error)"))
             }
         default:
             return .failure(.unknownError("Unhandled header type: \(message.headerType)"))