+///
+/// FileMonitor, a file monitor based on QFileSystemWatcher
+///
+
+class FileMonitor;
+class ActiveFileMonitor;
+class FileMonitorGuard;
+typedef std::unique_ptr<FileMonitor> FileMonitorPtr;
+typedef std::unique_ptr<ActiveFileMonitor> ActiveFileMonitorPtr;
+
+///
+/// Watch a file:
+/// FileMonitorPtr monitor = FileSystemWatcher::monitor(file_with_path);
+/// monitor.connect(...); //(using boost::signals2), or:
+/// connect(monitor, SIGNAL(fileChanged()),...); // (using Qt)
+///
+/// Remember that a unique_ptr is automatically deleted at the end of a scope if
+/// it has not been moved, or when assigned. When that happens, the signal
+/// object is deleted and therefore all the connections are closed. The file
+/// ceases being tracked when all the monitors for a file have been deleted.
+///
+/// Stop watching:
+/// * as determined statically by the scope, or
+/// * dynamically, using:
+/// monitor = nullptr;
+///
+/// Watch a different file:
+/// monitor = FileSystemWatcher::monitor(file_with_path2);
+/// monitor.connect(...);
+/// (stops watching the first)
+///
+class FileSystemWatcher