Refactor structure of GetTypeForBuffers for Type::DICTIONARY

cpp/src/arrow/util/align_util.cc

@@ -43,29 +43,25 @@ namespace {
 // Returns the type that controls how the buffers of this ArrayData (not its children)
 // should behave
 Type::type GetTypeForBuffers(const ArrayData& array) {
-  Type::type type_id = array.type->id();
-  Type::type storage_type_id = array.type->storage_id();
-  if (storage_type_id == Type::DICTIONARY) {
-    switch (type_id) {
+  Type::type type_id = array.type->storage_id();
+  if (type_id == Type::DICTIONARY) {
+    std::shared_ptr<DataType> dict_type;
+    switch (array.type->id()) {
       case Type::DICTIONARY:
-        storage_type_id =
-            ::arrow::internal::checked_pointer_cast<DictionaryType>(array.type)
-                ->index_type()
-                ->id();
+        dict_type = array.type;
         break;
       case Type::EXTENSION: {
-        auto dictExtType =
-            ::arrow::internal::checked_pointer_cast<ExtensionType>(array.type);
-        storage_type_id = ::arrow::internal::checked_pointer_cast<DictionaryType>(
-                              dictExtType->storage_type())
-                              ->index_type()
-                              ->id();
+        const auto ext_type = ::arrow::internal::checked_pointer_cast<ExtensionType>(array.type);
+        dict_type = ext_type->storage_type();
       } break;
       default:
         break;
     }
+    return ::arrow::internal::checked_pointer_cast<DictionaryType>(dict_type)
+        ->index_type()
+        ->id();
   }
-  return storage_type_id;
+  return type_id;
 }
 
 // Checks to see if an array's own buffers are aligned but doesn't check