static cast handle for rtrn_valu works by simply dropping in code from...

static cast handle for rtrn_valu works by simply dropping in code from type_caster_base (marked with comments). rtrn_rref raises a RuntimeError, to be investigated.

tests/test_classh_wip.cpp

@@ -74,8 +74,12 @@ struct type_caster<mpty> : smart_holder_type_caster_load<mpty> {
     // static handle cast(mpty, ...)
     // is redundant (leads to ambiguous overloads).
 
-    static handle cast(mpty && /*src*/, return_value_policy /*policy*/, handle /*parent*/) {
-        return str("cast_rref").release();
+    static handle cast(mpty &&src, return_value_policy /*policy*/, handle parent) {
+        // type_caster_base BEGIN
+        // clang-format off
+        return cast(&src, return_value_policy::move, parent);
+        // clang-format on
+        // type_caster_base END
     }
 
     static handle cast(mpty const &src, return_value_policy policy, handle parent) {

tests/test_classh_wip.py

@@ -14,14 +14,21 @@ def test_mpty_constructors():
 
 
 def test_cast():
-    assert m.rtrn_mpty_valu() == "cast_rref"
-    assert m.rtrn_mpty_rref() == "cast_rref"
+    assert m.get_mtxt(m.rtrn_mpty_valu()) == "rtrn_valu"
+    #                                         rtrn_rref exercised separately.
     assert m.get_mtxt(m.rtrn_mpty_cref()) == "rtrn_cref"
     assert m.get_mtxt(m.rtrn_mpty_mref()) == "rtrn_mref"
     assert m.get_mtxt(m.rtrn_mpty_cptr()) == "rtrn_cptr"
     assert m.get_mtxt(m.rtrn_mpty_mptr()) == "rtrn_mptr"
 
 
+def test_cast_rref():
+    e = m.rtrn_mpty_rref()
+    assert e.__class__.__name__ == "mpty"
+    with pytest.raises(RuntimeError):
+        m.get_mtxt(e)  # E.g. basic_string::_M_construct null not valid
+
+
 def test_load():
     assert m.pass_mpty_valu(m.mpty("Valu")) == "pass_valu:Valu"
     assert m.pass_mpty_rref(m.mpty("Rref")) == "pass_rref:Rref"