allow changing the number of root nodes

packages/core/src/create.rs

@@ -25,6 +25,10 @@ impl<'b> VirtualDom {
 
     /// Create this template and write its mutations
     pub(crate) fn create(&mut self, node: &'b VNode<'b>) -> usize {
+        // Intialize the root nodes slice
+        node.root_ids
+            .intialize(vec![ElementId(0); node.template.get().roots.len()].into_boxed_slice());
+
         // The best renderers will have templates prehydrated and registered
         // Just in case, let's create the template using instructions anyways
         if !self.templates.contains_key(&node.template.get().name) {
@@ -213,7 +217,7 @@ impl<'b> VirtualDom {
     fn load_template_root(&mut self, template: &VNode, root_idx: usize) -> ElementId {
         // Get an ID for this root since it's a real root
         let this_id = self.next_root(template, root_idx);
-        template.root_ids[root_idx].set(Some(this_id));
+        template.root_ids.set(root_idx, this_id);
 
         self.mutations.push(LoadTemplate {
             name: template.template.get().name,