[core] Avoid copying feature propertiesupstream/mikhail_avoid_feature_properties_copying

1 files changed, 2 insertions, 1 deletions

diff --git a/src/mbgl/style/expression/compound_expression.cpp b/src/mbgl/style/expression/compound_expression.cpp
index cc1d58025b..34f0f5dea3 100644
--- a/src/mbgl/style/expression/compound_expression.cpp
+++ b/src/mbgl/style/expression/compound_expression.cpp
@@ -423,7 +423,8 @@ const auto& propertiesCompoundExpression() {
             };
         }
         std::unordered_map<std::string, Value> result;
-        const PropertyMap properties = params.feature->getProperties();
+        const PropertyMap& properties = params.feature->getProperties();
+        result.reserve(properties.size());
         for (const auto& entry : properties) {
             result[entry.first] = toExpressionValue(entry.second);
         }