ARROW-10121: [C++] Fix emission of new dictionaries in IPC writer

cpp/src/arrow/ipc/CMakeLists.txt

@@ -45,8 +45,9 @@ function(ADD_ARROW_IPC_TEST REL_TEST_NAME)
 endfunction()
 
 add_arrow_test(feather_test)
-add_arrow_ipc_test(read_write_test)
 add_arrow_ipc_test(json_simple_test)
+add_arrow_ipc_test(read_write_test)
+add_arrow_ipc_test(tensor_test)
 
 # Headers: top level
 arrow_install_all_headers("arrow/ipc")

cpp/src/arrow/ipc/dictionary.cc

@@ -236,10 +236,19 @@ Status DictionaryMemo::AddDictionaryDelta(int64_t id,
   return Status::OK();
 }
 
-Status DictionaryMemo::AddOrReplaceDictionary(
+Result<bool> DictionaryMemo::AddOrReplaceDictionary(
     int64_t id, const std::shared_ptr<ArrayData>& dictionary) {
-  impl_->id_to_dictionary_[id] = {dictionary};
-  return Status::OK();
+  ArrayDataVector value{dictionary};
+
+  auto pair = impl_->id_to_dictionary_.emplace(id, value);
+  if (pair.second) {
+    // Inserted
+    return true;
+  } else {
+    // Update existing value
+    pair.first->second = std::move(value);
+    return false;
+  }
 }
 
 // ----------------------------------------------------------------------

cpp/src/arrow/ipc/dictionary.h

@@ -133,7 +133,10 @@ class ARROW_EXPORT DictionaryMemo {
 
   /// \brief Add a dictionary to the memo if it does not have one with the id,
   /// otherwise, replace the dictionary with the new one.
-  Status AddOrReplaceDictionary(int64_t id, const std::shared_ptr<ArrayData>& dictionary);
+  ///
+  /// Return true if the dictionary was added, false if replaced.
+  Result<bool> AddOrReplaceDictionary(int64_t id,
+                                      const std::shared_ptr<ArrayData>& dictionary);
 
  private:
   struct Impl;