add c++17 guard

include/pybind11/cast.h

@@ -1329,14 +1329,18 @@ object object_or_cast(T &&o) {
     return pybind11::cast(std::forward<T>(o));
 }
 
+
+#if defined(PYBIND11_CPP17)
 // Declared in pytypes.h:
 // Written here so make_caster<T> can be used
 template <typename D>
 template <typename T>
 str_attr_accessor object_api<D>::attr_with_type(const char *key) const {
-    annotations()[key] = make_caster<T>::name.text;
+    static constexpr auto name = make_caster<T>::name;
+    annotations()[key] = name.text;
     return {derived(), key};
 }
+#endif
 
 // Placeholder type for the unneeded (and dead code) static variable in the
 // PYBIND11_OVERRIDE_OVERRIDE macro

include/pybind11/pytypes.h

@@ -113,10 +113,11 @@ class object_api : public pyobject_tag {
     /// See above (the only difference is that the key is provided as a string literal)
     str_attr_accessor attr(const char *key) const;
 
+#if defined(PYBIND11_CPP17)
     // attr_with_type is implemented in cast.h:
     template <typename T>
     str_attr_accessor attr_with_type(const char *key) const;
-
+#endif
     /** \rst
         Matches * unpacking in Python, e.g. to unpack arguments out of a ``tuple``
         or ``list`` for a function call. Applying another * to the result yields