Be sure to properly treat both rvalues and lvalues in c2py functions

Author: Wentzell

c++/cpp2py/converters/map.hpp

@@ -1,17 +1,28 @@
 #pragma once
 #include <map>
+#include "../traits.hpp"
 
 namespace cpp2py {
 
   template <typename K, typename V> struct py_converter<std::map<K, V>> {
 
-    static PyObject *c2py(std::map<K, V> const &m) {
+    template <typename M> static PyObject *c2py(M &&m) {
+      static_assert(is_instantiation_of_v<std::map, std::decay_t<M>>, "Logic Error");
+
       PyObject *d = PyDict_New();
-      for (auto &x : m) {
-        pyref k = py_converter<K>::c2py(x.first);
+      for (auto &[key, val] : m) {
+        pyref k, v;
+        if constexpr (std::is_reference_v<M>) {
+          k = convert_to_python(key);
+          v = convert_to_python(val);
+        } else { // Map passed as rvalue
+          k = convert_to_python(std::move(key));
+          v = convert_to_python(std::move(val));
+        }
+
         // if the K is a list, we transform into a tuple
         if (PyList_Check(k)) k = PyList_AsTuple(k);
-        pyref v = py_converter<V>::c2py(x.second);
+
         if (k.is_null() or v.is_null() or (PyDict_SetItem(d, k, v) == -1)) {
           Py_DECREF(d);
           return NULL;

c++/cpp2py/converters/optional.hpp

@@ -1,14 +1,17 @@
 #pragma once
+#include "../traits.hpp"
+
 namespace cpp2py {
 
  template <typename T> struct py_converter<std::optional<T>> {
 
-  using conv = py_converter<T>;
+   using conv = py_converter<std::decay_t<T>>;
 
-  static PyObject *c2py(std::optional<T> &op) {
-   if (!bool(op)) Py_RETURN_NONE;
-   return conv::c2py(*op);
-  }
+   template <typename O> static PyObject *c2py(O &&op) {
+     static_assert(is_instantiation_of_v<std::optional, std::decay_t<O>>, "Logic Error");
+     if (!bool(op)) Py_RETURN_NONE;
+     return conv::c2py(*(std::forward<O>(op)));
+   }
 
   static bool is_convertible(PyObject *ob, bool raise_exception) {
    return ((ob == Py_None) or conv::is_convertible(ob, raise_exception));

c++/cpp2py/converters/pair.hpp

@@ -1,13 +1,15 @@
 #pragma once
-//#include <utility>
+#include "../traits.hpp"
 
 namespace cpp2py {
 
   template <typename T1, typename T2> struct py_converter<std::pair<T1, T2>> {
 
-    static PyObject *c2py(std::pair<T1, T2> const &p) {
-      pyref x1 = py_converter<T1>::c2py(std::get<0>(p));
-      pyref x2 = py_converter<T2>::c2py(std::get<1>(p));
+    template <typename P> static PyObject *c2py(P &&p) {
+      static_assert(is_instantiation_of_v<std::pair, std::decay_t<P>>, "Logic error");
+      pyref x1 = convert_to_python(std::get<0>(std::forward<P>(p)));
+      pyref x2 = convert_to_python(std::get<1>(std::forward<P>(p)));
+
       if (x1.is_null() or x2.is_null()) return NULL;
       return PyTuple_Pack(2, (PyObject *)x1, (PyObject *)x2);
     }

c++/cpp2py/converters/set.hpp

@@ -1,14 +1,21 @@
 #pragma once
 #include <set>
+#include "../traits.hpp"
 
 namespace cpp2py {
 
   template <typename K> struct py_converter<std::set<K>> {
 
-    static PyObject *c2py(std::set<K> const &s) {
+    template <typename S> static PyObject *c2py(S &&s) {
+      static_assert(is_instantiation_of_v<std::set, std::decay_t<S>>, "Logic error");
       PyObject *set = PySet_New(NULL);
       for (auto &x : s) {
-        pyref y = py_converter<K>::c2py(x);
+        pyref y;
+        if constexpr (std::is_reference_v<S>) {
+          y = convert_to_python(x);
+        } else { // s passed as rvalue
+          y = convert_to_python(std::move(x));
+        }
         if (y.is_null() or (PySet_Add(set, y) == -1)) {
           Py_DECREF(set);
           return NULL;
@@ -31,7 +38,7 @@ namespace cpp2py {
       if (raise_exception) { PyErr_SetString(PyExc_TypeError, "Cannot convert to std::set"); }
       return false;
     }
- 
+
     static std::set<K> py2c(PyObject *ob) {
       std::set<K> res;
       pyref keys_it = PyObject_GetIter(ob);

c++/cpp2py/converters/tuple.hpp

@@ -3,6 +3,8 @@
 #include <tuple>
 #include <numeric>
 
+#include "../traits.hpp"
+
 namespace cpp2py {
 
   template <typename... Types> struct py_converter<std::tuple<Types...>> {
@@ -11,28 +13,29 @@ namespace cpp2py {
     using tuple_t = std::tuple<Types...>;
 
     // c2py implementation
-    template <std::size_t... Is> static PyObject *c2py_impl(tuple_t const &t, std::index_sequence<Is...>) {
-      auto objs        = std::array<pyref, sizeof...(Is)>{pyref(py_converter<Types>::c2py(std::get<Is>(t)))...};
+    template <typename T, auto... Is> static PyObject *c2py_impl(T &&t, std::index_sequence<Is...>) {
+      auto objs        = std::array<pyref, sizeof...(Is)>{convert_to_python(std::get<Is>(std::forward<T>(t)))...};
       bool one_is_null = std::accumulate(std::begin(objs), std::end(objs), false, [](bool x, PyObject *a) { return x or (a == NULL); });
       if (one_is_null) return NULL;
       return PyTuple_Pack(sizeof...(Types), (PyObject *)(objs[Is])...);
     }
 
     // is_convertible implementation
-    template <int N, typename T, typename... Tail> static bool is_convertible_impl(PyObject *seq, bool raise_exception) {
-      return py_converter<T>::is_convertible(PySequence_Fast_GET_ITEM(seq, N), raise_exception)
-         && is_convertible_impl<N + 1, Tail...>(seq, raise_exception);
+    template <auto... Is> static bool is_convertible_impl(PyObject *seq, bool raise_exception, std::index_sequence<Is...>) {
+      return (py_converter<std::decay_t<Types>>::is_convertible(PySequence_Fast_GET_ITEM(seq, Is), raise_exception) and ...);
     }
-    template <int> static bool is_convertible_impl(PyObject *seq, bool raise_exception) { return true; }
 
-    template <size_t... Is> static auto py2c_impl(std::index_sequence<Is...>, PyObject *seq) {
-      return std::make_tuple(py_converter<Types>::py2c(PySequence_Fast_GET_ITEM(seq, Is))...);
+    template <auto... Is> static auto py2c_impl(PyObject *seq, std::index_sequence<Is...>) {
+      return std::make_tuple(py_converter<std::decay_t<Types>>::py2c(PySequence_Fast_GET_ITEM(seq, Is))...);
     }
 
     public:
     // -----------------------------------------
 
-    static PyObject *c2py(tuple_t const &t) { return c2py_impl(t, std::make_index_sequence<sizeof...(Types)>()); }
+    template <typename T> static PyObject *c2py(T &&t) {
+      static_assert(is_instantiation_of_v<std::tuple, std::decay_t<T>>, "Logic Error");
+      return c2py_impl(std::forward<T>(t), std::make_index_sequence<sizeof...(Types)>());
+    }
 
     // -----------------------------------------
 
@@ -41,7 +44,7 @@ namespace cpp2py {
         pyref seq = PySequence_Fast(ob, "expected a sequence");
         // Sizes must match! Could we relax this condition to '<'?
         if (PySequence_Fast_GET_SIZE((PyObject *)seq) != std::tuple_size<tuple_t>::value) goto _false;
-        if (!is_convertible_impl<0, Types...>((PyObject *)seq, raise_exception)) goto _false;
+        if (!is_convertible_impl((PyObject *)seq, raise_exception, std::make_index_sequence<sizeof...(Types)>())) goto _false;
         return true;
       }
     _false:
@@ -53,7 +56,7 @@ namespace cpp2py {
 
     static tuple_t py2c(PyObject *ob) {
       pyref seq = PySequence_Fast(ob, "expected a sequence");
-      return py2c_impl(std::make_index_sequence<sizeof...(Types)>(), (PyObject *)seq);
+      return py2c_impl((PyObject *)seq, std::make_index_sequence<sizeof...(Types)>());
     }
   };
 } // namespace cpp2py

c++/cpp2py/converters/variant.hpp

@@ -2,6 +2,8 @@
 #include <tuple>
 #include <variant>
 
+#include "../traits.hpp"
+
 namespace cpp2py {
 
   // std::variant<T...> converter
@@ -45,18 +47,17 @@ namespace cpp2py {
     }
 
     struct _visitor {
-      template <typename U> PyObject *operator()(U const &x) { return py_converter<U>::c2py(x); }
+      template <typename U> PyObject *operator()(U &&x) { return convert_to_python(std::forward<U>(x)); }
     };
 
     public:
-    static PyObject *c2py(std::variant<T...> const &v) {
-      //auto l = [](auto const &x) -> PyObject * { return py_converter<decltype(x)>::c2py(x); };
-      return visit(_visitor{}, v);
-      //return visit(_visitor{}, v);
+    template <typename V> static PyObject *c2py(V &&v) {
+      static_assert(is_instantiation_of_v<std::variant, std::decay_t<V>>);
+      return visit(_visitor{}, std::forward<V>(v));
     }
 
     static bool is_convertible(PyObject *ob, bool raise_exception) {
-      if ((...  or py_converter<T>::is_convertible(ob, false))) return true;
+      if ((... or py_converter<std::decay_t<T>>::is_convertible(ob, false))) return true;
       if (raise_exception) { PyErr_SetString(PyExc_TypeError, "Cannot convert to std::variant"); }
       return false;
     }

c++/cpp2py/converters/vector.hpp

@@ -3,29 +3,30 @@
 #include <string>
 #include <numpy/arrayobject.h>
 
+#include "../traits.hpp"
 #include "../macros.hpp"
 #include "../numpy_proxy.hpp"
 
 namespace cpp2py {
 
-  template <typename T> static void delete_pycapsule(PyObject *capsule) {
-    auto *ptr = static_cast<std::unique_ptr<T[]> *>(PyCapsule_GetPointer(capsule, "guard"));
-    delete ptr;
-  }
-
   // Convert vector to numpy_proxy, WARNING: Deep Copy
-  template <typename T> numpy_proxy make_numpy_proxy_from_vector(std::vector<T> const &v) {
+  template <typename V> numpy_proxy make_numpy_proxy_from_vector(V &&v) {
+    static_assert(is_instantiation_of_v<std::vector, std::decay_t<V>>, "Logic error");
+    using value_type = typename std::remove_reference_t<V>::value_type;
 
-    auto *data_ptr = new std::unique_ptr<T[]>{new T[v.size()]};
-    std::copy(begin(v), end(v), data_ptr->get());
-    auto capsule = PyCapsule_New(data_ptr, "guard", &delete_pycapsule<T>);
+    auto *vec_heap        = new std::vector<value_type>{std::forward<V>(v)};
+    auto delete_pycapsule = [](PyObject *capsule) {
+      auto *ptr = static_cast<std::vector<value_type> *>(PyCapsule_GetPointer(capsule, "guard"));
+      delete ptr;
+    };
+    PyObject *capsule = PyCapsule_New(vec_heap, "guard", delete_pycapsule);
 
     return {1, // rank
-            npy_type<std::remove_const_t<T>>,
-            (void *)data_ptr->get(),
-            std::is_const_v<T>,
-            v_t{static_cast<long>(v.size())}, // extents
-            v_t{sizeof(T)},                   // strides
+            npy_type<value_type>,
+            (void *)vec_heap->data(),
+            std::is_const_v<value_type>,
+            std::vector<long>{long(vec_heap->size())}, // extents
+            std::vector<long>{sizeof(value_type)},     // strides
             capsule};
   }
 
@@ -50,14 +51,21 @@ namespace cpp2py {
 
   template <typename T> struct py_converter<std::vector<T>> {
 
-    static PyObject *c2py(std::vector<T> const &v) {
+    template <typename V> static PyObject *c2py(V &&v) {
+      static_assert(is_instantiation_of_v<std::vector, std::decay_t<V>>, "Logic error");
+      using value_type = typename std::remove_reference_t<V>::value_type;
 
-      if constexpr (has_npy_type<T>) {
-        return make_numpy_proxy_from_vector(v).to_python();
+      if constexpr (has_npy_type<value_type>) {
+        return make_numpy_proxy_from_vector(std::forward<V>(v)).to_python();
       } else { // Convert to Python List
         PyObject *list = PyList_New(0);
-        for (auto const &x : v) {
-          pyref y = py_converter<T>::c2py(x);
+        for (auto &x : v) {
+	  pyref y;
+	  if constexpr(std::is_reference_v<V>){
+            y = py_converter<value_type>::c2py(x);
+	  } else { // Vector passed as rvalue
+            y = py_converter<value_type>::c2py(std::move(x));
+	  }
           if (y.is_null() or (PyList_Append(list, y) == -1)) {
             Py_DECREF(list);
             return NULL;
@@ -122,7 +130,7 @@ namespace cpp2py {
       std::vector<T> res;
       pyref seq = PySequence_Fast(ob, "expected a sequence");
       int len   = PySequence_Size(ob);
-      for (int i = 0; i < len; i++) res.push_back(py_converter<T>::py2c(PySequence_Fast_GET_ITEM((PyObject *)seq, i))); //borrowed ref
+      for (int i = 0; i < len; i++) res.push_back(py_converter<std::decay_t<T>>::py2c(PySequence_Fast_GET_ITEM((PyObject *)seq, i))); //borrowed ref
       return res;
     }
   };

c++/cpp2py/numpy_proxy.hpp

@@ -9,15 +9,13 @@
 
 namespace cpp2py {
 
-  using v_t = std::vector<long>;
-
   // the basic information for a numpy array
   struct numpy_proxy {
     int rank          = 0;
     long element_type = 0;
     void *data        = nullptr;
     bool is_const     = false;
-    v_t extents, strides;
+    std::vector<long> extents, strides;
     PyObject *base = nullptr; // The ref. counting guard typically
 
     // Returns a new ref (or NULL if failure) with a new numpy.

c++/cpp2py/py_converter.hpp

@@ -127,6 +127,8 @@ namespace cpp2py {
 
     using is_wrapped_type = void; // to recognize
 
+    static_assert(not std::is_reference_v<T>, "Not implemented");
+
     template <typename U> static PyObject *c2py(U &&x) {
       PyTypeObject *p = get_type_ptr(typeid(T));
       if (p == nullptr) return NULL;

c++/cpp2py/pyref.hpp

@@ -131,6 +131,7 @@ namespace cpp2py {
       return i;
     }
   };
+  static_assert(sizeof(pyref) == sizeof(PyObject *), "pyref must contain only a PyObject *");
 
   // FIXME : put static or the other functions inline ?
 

c++/cpp2py/traits.hpp

@@ -0,0 +1,11 @@
+#pragma once
+#include <type_traits>
+
+namespace cpp2py {
+
+  template <template <typename...> class TMPLT, typename T> struct is_instantiation_of : std::false_type {};
+  template <template <typename...> class TMPLT, typename... U> struct is_instantiation_of<TMPLT, TMPLT<U...>> : std::true_type {};
+  template <template <typename...> class gf, typename T>
+  inline constexpr bool is_instantiation_of_v = is_instantiation_of<gf, std::decay_t<T>>::value;
+
+} // namespace cpp2py