properly perserving string pointers when merging time series

Author: Jofkos

plotjuggler_base/include/PlotJuggler/plotdatabase.h

@@ -373,7 +373,7 @@ class PlotDataBase
   }
 
 
-  void mergeWith(PlotDataBase<TypeX, Value>& other) {
+  virtual void mergeWith(PlotDataBase<TypeX, Value>& other) {
     if (other._points.empty())
       return;
 
@@ -396,17 +396,16 @@ class PlotDataBase
     }
 
     if constexpr (std::is_arithmetic_v<TypeX>) {
+      // new points are all before this->_points
+      if (other._points.back().x < this->_points.front().x) {
+        this->_points.swap(other._points);
+      }
 
       // new points are all after this->_points
       if (other._points.front().x > this->_points.back().x) {
         std::move(other._points.begin(), other._points.end(), std::back_inserter(this->_points));
-
-                // new points are all before this->_points
-      } else if (other._points.back().x < this->_points.front().x) {
-        std::move(this->_points.begin(), this->_points.end(), std::back_inserter(other._points));
-        this->_points.swap(other._points);
       } else {
-        // Fallback to standard merging with move where possible
+        // Overlap: fallback to standard merging with move where possible
         std::deque<Point> result;
         std::merge(std::make_move_iterator(this->_points.begin()), std::make_move_iterator(this->_points.end()),
                    std::make_move_iterator(other._points.begin()), std::make_move_iterator(other._points.end()),

plotjuggler_base/include/PlotJuggler/stringseries.h

@@ -70,6 +70,28 @@ class StringSeries : public TimeseriesBase<StringRef>
     }
   }
 
+  virtual void mergeWith(PlotDataBase<double, StringRef>& other) override {
+    StringSeries* otherStringSeries = dynamic_cast<StringSeries*>(&other);
+    if (otherStringSeries) {
+      for (auto& pointRef : other) {
+        if (pointRef.y.isSSO()){
+          continue;
+        }
+
+        _tmp_str.assign(pointRef.y.data(), pointRef.y.size());
+
+        auto it = _storage.find(_tmp_str);
+        if (it == _storage.end())
+        {
+          it = _storage.insert(_tmp_str).first;
+        }
+
+        pointRef.y = std::move(StringRef(*it)); // point pointers to this here storage
+      }
+    }
+    PlotDataBase<double, StringRef>::mergeWith(other);
+  }
+
 private:
   std::string _tmp_str;
   std::unordered_set<std::string> _storage;