Fix build on latest AppleClang (#629)

include/treelite/c_api.h

@@ -139,7 +139,7 @@ TREELITE_DLL int TreeliteLoadXGBoostModelUBJSON(
  * \return 0 for success, -1 for failure
  */
 TREELITE_DLL int TreeliteLoadXGBoostModelFromUBJSONString(
-    uint8_t const* ubjson_str, size_t length, char const* config_json, TreeliteModelHandle* out);
+    char const* ubjson_str, size_t length, char const* config_json, TreeliteModelHandle* out);
 /*!
  * \brief Inspect the first few bytes of an XGBoost model and heuristically determine whether
  *        it's using the JSON or UBJSON format.

include/treelite/model_loader.h

@@ -72,7 +72,7 @@ std::unique_ptr<treelite::Model> LoadXGBoostModelUBJSON(
  * \return Loaded model
  */
 std::unique_ptr<treelite::Model> LoadXGBoostModelFromUBJSONString(
-    std::basic_string_view<std::uint8_t> ubjson_str, std::string const& config_json);
+    std::string_view ubjson_str, std::string const& config_json);
 
 /*!
  * \brief Inspect the first few bytes of an XGBoost model and heuristically determine whether

src/c_api/model_loader.cc

@@ -78,11 +78,11 @@ int TreeliteLoadXGBoostModelUBJSON(
   API_END();
 }
 
-int TreeliteLoadXGBoostModelFromUBJSONString(std::uint8_t const* ubjson_str, std::size_t length,
-    char const* config_json, TreeliteModelHandle* out) {
+int TreeliteLoadXGBoostModelFromUBJSONString(
+    char const* ubjson_str, std::size_t length, char const* config_json, TreeliteModelHandle* out) {
   API_BEGIN();
   std::unique_ptr<treelite::Model> model = treelite::model_loader::LoadXGBoostModelFromUBJSONString(
-      std::basic_string_view<std::uint8_t>{ubjson_str, length}, config_json);
+      std::string_view{ubjson_str, length}, config_json);
   *out = static_cast<TreeliteModelHandle>(model.release());
   API_END();
 }

src/model_loader/xgboost_ubjson.cc

@@ -37,7 +37,7 @@ std::unique_ptr<treelite::Model> LoadXGBoostModelUBJSON(
 }
 
 std::unique_ptr<treelite::Model> LoadXGBoostModelFromUBJSONString(
-    std::basic_string_view<std::uint8_t> ubjson_str, std::string const& config_json) {
+    std::string_view ubjson_str, std::string const& config_json) {
   nlohmann::json parsed_config = nlohmann::json::parse(config_json);
   return ParseStream(ubjson_str, parsed_config);
 }