draft the determineBackend() routine

src/PTQ/PTQ.cpp

@@ -111,6 +111,35 @@ static std::shared_ptr<Aidge::Node> getUniqueChildren(std::shared_ptr<Aidge::Nod
     return *(childrenSet.begin());
 }
 
+static std::string determineBackend(std::shared_ptr<Aidge::Node> node)
+{
+    std::string backend = node->getOperator()->backend();
+
+    if (backend != "")
+        return backend;
+    else 
+    {
+        // gather the parent backends
+
+        std::set<std::string> parentBackends;
+        for (auto parent : node->getParents())
+            parentBackends.insert(determineBackend(parent)); // it always answers a non empty value !
+
+        // check if we have two or more different backends gathered
+
+        if (parentBackends.size() > 1) 
+        {
+            Log::warn(" Unable to determine backend of node {} due to conflicting parent ones !", node->name());
+            return (*parentBackends.begin());
+        }
+        
+        // if all parents have the same backend return it
+
+        if (parentBackends.size() == 1) 
+            return (*parentBackends.begin());
+    }
+}
+
 static int getInputIndex(std::shared_ptr<Node> node, std::shared_ptr<Node> parentNode)
 {
     int index = 0;