HACK for clang: Remove protection for operator type()

While for gcc, I need to SFINAE-restrict the cast operator: `operator type() { return std::move(value); }`
to move-constructible types, clang fails with this protection, claiming that the cast operator isn't
created for e.g. std::string - although it is move-constructible.

Turns out, that it works on clang w/o the SFINAE protection, but then fails on gcc again. I didn't
look into MSVC yet.

Author: rhaschke

include/pybind11/cast.h

@@ -952,8 +952,7 @@ template <typename type> class type_caster_base : public type_caster_generic {
     // move-forward caster, just forwarding an rvalue reference
     operator itype&&() { if (!value) throw reference_cast_error(); return std::move(*((itype *) value)); }
     // move caster, actually triggering a move construction from value
-    template <typename T_ = itype, enable_if_t<std::is_move_constructible<T_>::value, int> = 0>
-    operator T_() { if (!value) throw reference_cast_error(); return std::move(*((itype *) value)); }
+    operator itype() { if (!value) throw reference_cast_error(); return std::move(*((itype *) value)); }
 
 protected:
     using Constructor = void *(*)(const void *);
@@ -1029,8 +1028,7 @@ template <typename type> class type_caster<std::reference_wrapper<type>> {
         operator type*() { return &value; } \
         operator type&() { return value; } \
         operator type&&() { return std::move(value); } \
-        template <typename T_ = type, enable_if_t<std::is_move_constructible<T_>::value, int> = 0> \
-        operator T_() { return std::move(value); } \
+        operator type() { return std::move(value); } \
         template <typename T_> using cast_op_type = pybind11::detail::movable_cast_op_type<T_>
 
 

tests/test_copy_move.py

@@ -125,9 +125,9 @@ def test_move_and_copy_load_optional():
     assert c_m.move_assignments == 2
     assert c_m.move_constructions == 6
     assert c_mc.copy_assignments == 0
-    assert c_mc.copy_constructions == 1
+    assert c_mc.copy_constructions == 2
     assert c_mc.move_assignments == 3
-    assert c_mc.move_constructions == 8
+    assert c_mc.move_constructions == 7
     assert c_c.copy_assignments == 2
     assert c_c.copy_constructions == 5
     assert c_m.alive() + c_mc.alive() + c_c.alive() == 0