fixup! Define two helper functions for for_each_successor

Author: romainbrenguier

src/solvers/refinement/string_refinement_util.cpp

@@ -375,18 +375,19 @@ void string_dependenciest::for_each_successor(
   const nodet &node,
   const std::function<void(const nodet &)> &f) const
 {
-  if(node.kind == nodet::BUILTIN)
+  switch(node.kind)
   {
-    for_each_dependency(
-      builtin_function_nodes[node.index],
-      [&](const string_nodet &n) { return f(nodet(n)); });
-  }
-  else
-  {
-    INVARIANT(node.kind == nodet::STRING, "nodes are either BUILTIN or STRING");
-    for_each_dependency(
-      string_nodes[node.index],
-      [&](const builtin_function_nodet &n) { return f(nodet(n)); });
+    case nodet::BUILTIN:
+      for_each_dependency(
+        builtin_function_nodes[node.index],
+        [&](const string_nodet &n) { return f(nodet(n)); });
+      break;
+
+    case nodet::STRING:
+      for_each_dependency(
+        string_nodes[node.index],
+        [&](const builtin_function_nodet &n) { return f(nodet(n)); });
+      break;
   }
 }