moving prototype code to pybind11/vptr_holder.h, adding type_caster specialization to make the bindings involving unique_ptr passing compile, but load and cast implementations are missing

include/pybind11/vptr_holder.h

@@ -0,0 +1,72 @@
+#pragma once
+
+#include <pybind11/pybind11.h>
+
+#include <memory>
+#include <variant>
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+// Could this be a holder for a `class_`-like `vclass`?
+// To enable passing of unique_ptr as in pure C++.
+template <typename T> class vptr {
+  public:
+    explicit vptr(T *ptr = nullptr) : vptr_{std::unique_ptr<T>(ptr)} {}
+    explicit vptr(std::unique_ptr<T> u) : vptr_{std::move(u)} {}
+    explicit vptr(std::shared_ptr<T> s) : vptr_{s} {}
+
+    int ownership_type() const {
+        if (std::get_if<0>(&vptr_)) {
+            return 0;
+        }
+        if (std::get_if<1>(&vptr_)) {
+            return 1;
+        }
+        return -1;
+    }
+
+    T *get() {
+        auto u = std::get_if<0>(&vptr_);
+        if (u) {
+            return u->get();
+        }
+        auto s = std::get_if<1>(&vptr_);
+        if (s) {
+            return s->get();
+        }
+        return nullptr;
+    }
+
+    std::unique_ptr<T> get_unique() {
+        auto u = std::get_if<0>(&vptr_);
+        if (u) {
+            return std::move(*u);
+        }
+        throw std::runtime_error("get_unique failure.");
+    }
+
+    std::shared_ptr<T> get_shared() {
+        auto s = std::get_if<1>(&vptr_);
+        if (s) {
+            return *s;
+        }
+        auto u = std::get_if<0>(&vptr_);
+        if (u) {
+            auto result = std::shared_ptr<T>(std::move(*u));
+            vptr_ = result;
+            return result;
+        }
+        throw std::runtime_error("get_shared failure.");
+    }
+
+  private:
+    std::variant<std::unique_ptr<T>, std::shared_ptr<T>> vptr_;
+};
+
+template <typename T> class vptr_holder : public vptr<T> {
+    using vptr<T>::vptr;
+};
+
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
+
+PYBIND11_DECLARE_HOLDER_TYPE(T, pybind11::vptr_holder<T>);

tests/test_unique_ptr_member.cpp

@@ -1,5 +1,7 @@
 #include "pybind11_tests.h"
 
+#include <pybind11/vptr_holder.h>
+
 #include <iostream>
 #include <memory>
 
@@ -66,17 +68,46 @@ inline int cpp_pattern() {
     return result;
 }
 
+} // namespace unique_ptr_member
+} // namespace pybind11_tests
+
+namespace pybind11 {
+namespace detail {
+template <>
+struct type_caster<
+    std::unique_ptr<pybind11_tests::unique_ptr_member::pointee>> {
+  public:
+    PYBIND11_TYPE_CASTER(
+        std::unique_ptr<pybind11_tests::unique_ptr_member::pointee>,
+        _("std::unique_ptr<pybind11_tests::unique_ptr_member::pointee>"));
+
+    bool load(handle /* src */, bool) {
+        throw std::runtime_error("Not implemented: load");
+    }
+
+    static handle
+    cast(std::unique_ptr<pybind11_tests::unique_ptr_member::pointee> /* src */,
+         return_value_policy /* policy */, handle /* parent */) {
+        throw std::runtime_error("Not implemented: cast");
+    }
+};
+} // namespace detail
+} // namespace pybind11
+
+namespace pybind11_tests {
+namespace unique_ptr_member {
+
 TEST_SUBMODULE(unique_ptr_member, m) {
     m.def("to_cout", to_cout);
 
-    py::class_<pointee, std::shared_ptr<pointee>>(m, "pointee")
+    py::class_<pointee, py::vptr_holder<pointee>>(m, "pointee")
         .def(py::init<>())
         .def("get_int", &pointee::get_int);
 
     m.def("make_unique_pointee", make_unique_pointee);
 
     py::class_<ptr_owner>(m, "ptr_owner")
-        //.def(py::init<std::unique_ptr<pointee>>(), py::arg("ptr"))
+        .def(py::init<std::unique_ptr<pointee>>(), py::arg("ptr"))
         .def("is_owner", &ptr_owner::is_owner)
         .def("give_up_ownership_via_unique_ptr",
              &ptr_owner::give_up_ownership_via_unique_ptr)

tests/test_variant_unique_shared.cpp

@@ -1,74 +1,22 @@
+#include "pybind11_tests.h"
+
+#include <pybind11/vptr_holder.h>
+
 #include <memory>
 #include <variant>
 
-#include "pybind11_tests.h"
-
 namespace pybind11_tests {
 
-// Could this be a holder for a `class_`-like `vclass`?
-// To enable passing of unique_ptr as in pure C++.
-template <typename T> class vptr_holder {
-  public:
-    explicit vptr_holder(T *ptr = nullptr) : vptr_{std::unique_ptr<T>(ptr)} {}
-    explicit vptr_holder(std::unique_ptr<T> u) : vptr_{std::move(u)} {}
-    explicit vptr_holder(std::shared_ptr<T> s) : vptr_{s} {}
+using pybind11::vptr;
 
-    int ownership_type() const {
-        if (std::get_if<0>(&vptr_)) {
-            return 0;
-        }
-        if (std::get_if<1>(&vptr_)) {
-            return 1;
-        }
-        return -1;
-    }
+vptr<double> from_raw() { return vptr<double>{new double{3}}; }
 
-    T *get() {
-        auto u = std::get_if<0>(&vptr_);
-        if (u) {
-            return u->get();
-        }
-        auto s = std::get_if<1>(&vptr_);
-        if (s) {
-            return s->get();
-        }
-        return nullptr;
-    }
-
-    std::unique_ptr<T> get_unique() {
-        auto u = std::get_if<0>(&vptr_);
-        if (u) {
-            return std::move(*u);
-        }
-        throw std::runtime_error("get_unique failure.");
-    }
-
-    std::shared_ptr<T> get_shared() {
-        auto s = std::get_if<1>(&vptr_);
-        if (s) {
-            return *s;
-        }
-        auto u = std::get_if<0>(&vptr_);
-        if (u) {
-            auto result = std::shared_ptr<T>(std::move(*u));
-            vptr_ = result;
-            return result;
-        }
-        throw std::runtime_error("get_shared failure.");
-    }
-
-  private:
-    std::variant<std::unique_ptr<T>, std::shared_ptr<T>> vptr_;
-};
-
-vptr_holder<double> from_raw() { return vptr_holder<double>{new double{3}}; }
-
-vptr_holder<double> from_unique() {
-    return vptr_holder<double>{std::unique_ptr<double>(new double{5})};
+vptr<double> from_unique() {
+    return vptr<double>{std::unique_ptr<double>(new double{5})};
 }
 
-vptr_holder<double> from_shared() {
-    return vptr_holder<double>{std::shared_ptr<double>(new double{7})};
+vptr<double> from_shared() {
+    return vptr<double>{std::shared_ptr<double>(new double{7})};
 }
 
 TEST_SUBMODULE(variant_unique_shared, m) {
@@ -77,22 +25,22 @@ TEST_SUBMODULE(variant_unique_shared, m) {
     m.def("from_unique", from_unique);
     m.def("from_shared", from_shared);
 
-    py::class_<vptr_holder<double>>(m, "vptr_holder_double")
+    py::class_<vptr<double>>(m, "vptr_double")
         .def(py::init<>())
-        .def("ownership_type", &vptr_holder<double>::ownership_type)
+        .def("ownership_type", &vptr<double>::ownership_type)
         .def("get_value",
-             [](vptr_holder<double> &v) {
+             [](vptr<double> &v) {
                  auto p = v.get();
                  if (p)
                      return *p;
                  return -1.;
              })
         .def("get_unique",
-             [](vptr_holder<double> &v) {
+             [](vptr<double> &v) {
                  v.get_unique();
                  return;
              })
-        .def("get_shared", [](vptr_holder<double> &v) {
+        .def("get_shared", [](vptr<double> &v) {
             v.get_shared();
             return;
         });

tests/test_variant_unique_shared.py

@@ -5,7 +5,7 @@ from pybind11_tests import variant_unique_shared as m
 
 
 def test_default_constructed():
-    v = m.vptr_holder_double()
+    v = m.vptr_double()
     assert v.ownership_type() == 0
     assert v.get_value() == -1