write.. -> const; cleaner -> mutable

GUI/Model/Files/DatafilesSet.cpp

@@ -97,7 +97,7 @@ void DatafilesSet::readFrom(QXmlStreamReader* r)
         throw std::runtime_error(r->errorString().toLatin1());
 }
 
-void DatafilesSet::writeDatafiles(const QString& projectDir)
+void DatafilesSet::writeDatafiles(const QString& projectDir) const
 {
     for (const auto* dfile_item : dfileItems())
         dfile_item->writeDatafiles(projectDir);

GUI/Model/Files/DatafilesSet.h

@@ -47,7 +47,7 @@ public:
 private:
     QVector<DataItem*> dataItems() const;
 
-    DatafilesCleaner dataFilesCleaner;
+    mutable DatafilesCleaner dataFilesCleaner;
     std::vector<std::unique_ptr<DatafileItem>> m_dfile_items;
     int m_current_index = -1;
 };