xo-gc stack: fix mutation setup + xo-reader2 utest

include/xo/object2/DArray.hpp

@@ -76,6 +76,11 @@ namespace xo {
             static DArray * _empty(obj<AAllocator> mm,
                                    size_type cap);
 
+            /** ofp version of _empty(mm,cap) **/
+            template <typename AFacet = AGCObject>
+            static obj<AFacet,DArray> empty(obj<AAllocator> mm,
+                                            size_type cap);
+
             /** create copy of @p src using memory from @p mm
              *  with capacity for @p new_cap elements
              **/
@@ -198,6 +203,15 @@ namespace xo {
             ///@}
         };
 
+        template <typename AFacet>
+        obj<AFacet,DArray>
+        DArray::empty(obj<AAllocator> mm, DArray::size_type cap)
+        {
+            DArray * retval = _empty(mm, cap);
+
+            return obj<AFacet,DArray>(retval);
+        }
+
         template <typename... Args>
             requires (std::convertible_to<Args, obj<DArray::AGCObject>> && ...)
         DArray *

src/object2/DArray.cpp

@@ -84,7 +84,8 @@ namespace xo {
         }
 
         bool
-        DArray::push_back(obj<AAllocator> mm, obj<AGCObject> elt) noexcept
+        DArray::push_back(obj<AAllocator> mm,
+                          obj<AGCObject> elt) noexcept
         {
             if (size_ >= capacity_) {
                 return false;

utest/DArray.test.cpp

@@ -63,6 +63,9 @@ namespace xo {
             auto alloc = with_facet<AAllocator>::mkobj(&arena);
             obj<AAllocator> null_mm;
 
+            REQUIRE(!null_mm.data());
+            REQUIRE(!null_mm._has_null_vptr()); // any
+
             DArray * arr = DArray::_empty(alloc, 16);
             REQUIRE(arr != nullptr);
             REQUIRE(arr->capacity() == 16);