From f14c783eb36aebe42862bf63e60afd048fb11a68 Mon Sep 17 00:00:00 2001
From: Jin Shang <shangjin1997@gmail.com>
Date: Sat, 23 Dec 2023 11:47:49 +0800
Subject: [PATCH] Update cpp/src/arrow/compute/kernels/vector_hash.cc

Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
---
 cpp/src/arrow/compute/kernels/vector_hash.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cpp/src/arrow/compute/kernels/vector_hash.cc b/cpp/src/arrow/compute/kernels/vector_hash.cc
index 4f16651013948..917f930ac5da3 100644
--- a/cpp/src/arrow/compute/kernels/vector_hash.cc
+++ b/cpp/src/arrow/compute/kernels/vector_hash.cc
@@ -500,6 +500,8 @@ class DictionaryHashKernel : public HashKernel {
     return dictionary_value_type_;
   }
 
+  /// This can't be called more than once because DictionaryUnifier::GetResult()
+  /// can't be called more than once and produce the same output. 
   Result<std::shared_ptr<Array>> dictionary() const {
     if (!first_dictionary_) {  // Append was never called
       return nullptr;