Use UNDEFINED and not 2**32-1

src/forest.cpp

@@ -74,28 +74,7 @@ Constructs a forest with *n* nodes, that is initialised so that the
                    parents,
                std::vector<std::variant<Forest::node_type, Undefined>> const&
                    labels) {
-              using node_type = Forest::node_type;
-              std::vector<node_type> parents_as_ints;
-              std::vector<node_type> labels_as_ints;
-              for (auto const& val : parents) {
-                if (std::holds_alternative<node_type>(val)) {
-                  parents_as_ints.push_back(std::get<0>(val));
-                } else {
-                  parents_as_ints.push_back(
-                      static_cast<node_type>(std::get<1>(val)));
-                }
-              }
-              // TODO there's something like this in transf.cpp too, we should
-              // avoid code dupl
-              for (auto const& val : labels) {
-                if (std::holds_alternative<node_type>(val)) {
-                  labels_as_ints.push_back(std::get<0>(val));
-                } else {
-                  labels_as_ints.push_back(
-                      static_cast<node_type>(std::get<1>(val)));
-                }
-              }
-              return make<Forest>(parents_as_ints, labels_as_ints);
+              return make<Forest>(to_ints(parents), to_ints(labels));
             }),
         py::arg("parents"),
         py::arg("labels"),

src/main.hpp

@@ -19,8 +19,12 @@
 #ifndef SRC_MAIN_HPP_
 #define SRC_MAIN_HPP_
 
+#include <variant>
+
 #include <pybind11/pybind11.h>
 
+#include <libsemigroups/constants.hpp>
+
 namespace libsemigroups {
 
   namespace py = pybind11;
@@ -70,6 +74,30 @@ namespace libsemigroups {
   void init_word_graph(py::module&);
   void init_words(py::module&);
 
+  template <typename Int>
+  std::vector<Int>
+  to_ints(std::vector<std::variant<Int, Undefined>> const& vec) {
+    std::vector<Int> vec_as_ints;
+    for (auto const& val : vec) {
+      if (std::holds_alternative<Int>(val)) {
+        vec_as_ints.push_back(std::get<0>(val));
+      } else {
+        vec_as_ints.push_back(static_cast<Int>(std::get<1>(val)));
+      }
+    }
+    return vec_as_ints;
+  }
+
+  template <typename Int>
+  std::vector<std::vector<Int>>
+  to_ints(std::vector<std::vector<std::variant<Int, Undefined>>> const& vec) {
+    std::vector<std::vector<Int>> vec_as_ints;
+    for (auto const& val : vec) {
+      vec_as_ints.push_back(to_ints(val));
+    }
+    return vec_as_ints;
+  }
+
 }  // namespace libsemigroups
 
 #endif  // SRC_MAIN_HPP_

src/transf.cpp

@@ -524,16 +524,7 @@ among the points where :math:`f` is defined).
       thing.def(
           py::init(
               [](std::vector<std::variant<Scalar, Undefined>> const& imgs) {
-                std::vector<Scalar> imgs_as_ints;
-                for (auto const& val : imgs) {
-                  if (std::holds_alternative<Scalar>(val)) {
-                    imgs_as_ints.push_back(std::get<0>(val));
-                  } else {
-                    imgs_as_ints.push_back(
-                        static_cast<Scalar>(std::get<1>(val)));
-                  }
-                }
-                return make<PPerm_>(std::move(imgs_as_ints));
+                return make<PPerm_>(to_ints(imgs));
               }),
           py::arg("imgs"),
           R"pbdoc(

src/word-graph.cpp

@@ -111,13 +111,15 @@ out-degree of any node is *n*. There are no edges in the defined word graph.
   :math:`O(mn)` where *m* is the number of nodes, and *n* is the
   out-degree of the word graph.)pbdoc");
 
-    thing.def(py::init([](size_t                                     num_nodes,
-                          std::vector<std::vector<node_type>> const& targets) {
-                return make<WordGraph_>(num_nodes, targets);
-              }),
-              py::arg("num_nodes"),
-              py::arg("targets"),
-              R"pbdoc(
+    thing.def(
+        py::init([](size_t                                          num_nodes,
+                    std::vector<std::vector<
+                        std::variant<node_type, Undefined>>> const& targets) {
+          return make<WordGraph_>(num_nodes, to_ints(targets));
+        }),
+        py::arg("num_nodes"),
+        py::arg("targets"),
+        R"pbdoc(
 Construct a word graph from a number of nodes and an list of targets.
 
 This function constructs a word graph from its arguments whose