use c++11 compatible code

Author: Rosdf

include/pybind11/detail/init.h

@@ -167,7 +167,7 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
                          "is not an alias instance");
     }
 
-    v_h.value_ptr<std::remove_pointer_t<decltype(ptr)>>() = ptr;
+    v_h.value_ptr<typename std::remove_pointer<decltype(ptr)>::type>() = ptr;
     v_h.type->init_instance(v_h.inst, &holder);
 }
 

include/pybind11/detail/value_and_holder.h

@@ -33,11 +33,7 @@ struct value_and_holder {
 
     template <typename V = void>
     V *&value_ptr() const {
-        if constexpr (std::is_const_v<V>) {
-            return reinterpret_cast<V *&>(const_cast<const void *&>(vh[0]));
-        } else {
-            return reinterpret_cast<V *&>(vh[0]);
-        }
+        return cast_void<V>(vh[0]);
     }
     // True if this `value_and_holder` has a non-null value pointer
     explicit operator bool() const { return value_ptr() != nullptr; }
@@ -76,6 +72,17 @@ struct value_and_holder {
             inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
         }
     }
+
+private:
+    template <typename V, detail::enable_if_t<!std::is_const<V>::value, bool> = true>
+    static V *&cast_void(void *&ptr) {
+        return reinterpret_cast<V *&>(ptr);
+    }
+
+    template <typename V, detail::enable_if_t<std::is_const<V>::value, bool> = true>
+    static V *&cast_void(void *&ptr) {
+        return reinterpret_cast<V *&>(const_cast<const void *&>(ptr));
+    }
 };
 
 // This is a semi-public API to check if the corresponding instance has been constructed with a