Special xetter_cpp_function::readonly to support m_valu_readonly.

Author: rwgk

include/pybind11/pybind11.h

@@ -1448,17 +1448,22 @@ struct xetter_cpp_function<
     template <typename PM>
     static cpp_function readonly(PM pm, const handle &hdl) {
         return cpp_function(
-            [pm](const std::shared_ptr<T> &c_sp) -> std::shared_ptr<D> {
-                // Emulating PyCLIF approach:
-                // https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
-                return std::shared_ptr<D>(c_sp, &(c_sp.get()->*pm));
+            [pm](const std::shared_ptr<T> &c_sp)
+                -> std::shared_ptr<typename std::add_const<D>::type> {
+                return std::shared_ptr<typename std::add_const<D>::type>(c_sp, &(c_sp.get()->*pm));
             },
             is_method(hdl));
     }
 
     template <typename PM>
     static cpp_function read(PM pm, const handle &hdl) {
-        return readonly(pm, hdl);
+        return cpp_function(
+            [pm](const std::shared_ptr<T> &c_sp) -> std::shared_ptr<D> {
+                // Emulating PyCLIF approach:
+                // https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
+                return std::shared_ptr<D>(c_sp, &(c_sp.get()->*pm));
+            },
+            is_method(hdl));
     }
 
     template <typename PM>

tests/test_class_sh_property.cpp

@@ -62,7 +62,7 @@ TEST_SUBMODULE(class_sh_property, m) {
 
     py::classh<Outer>(m, "Outer") //
         .def(py::init<>())        //
-        // .def_readonly("m_valu_readonly", &Outer::m_valu) //
+        .def_readonly("m_valu_readonly", &Outer::m_valu) //
         .def_readwrite("m_valu", &Outer::m_valu) //
         .def_property(                           //
             "m_mptr_property",