fix #65

Author: cmazakas

Diff for: libsafecxx/single-header/std2.h

@@ -827,6 +827,8 @@ box
   {
   }
 
+  box(box const^) = delete;
+
   [[unsafe::drop_only(T)]]
   ~box() safe {
     delete p_;

Diff for: libsafecxx/test/CMakeLists.txt

@@ -109,6 +109,7 @@ add_test(NAME "safecxx-verify-headers" COMMAND "${CMAKE_COMMAND}" --build ${CMAK
 safe_cxx_compile_fail_test(string_view1 "use of sv depends on expired loan")
 safe_cxx_compile_fail_test(box_incomplete "class incomplete is incomplete")
 safe_cxx_compile_fail_test(box1 "cannot convert prvalue int to std2::box<int>")
+safe_cxx_compile_fail_test(box2 "call to deleted borrow constructor")
 safe_cxx_compile_fail_test(arc1 "cannot convert prvalue int to std2::arc<int>")
 safe_cxx_compile_fail_test(rc1 "cannot convert prvalue int to std2::rc<int>")
 safe_cxx_compile_fail_test(unsafe_cell1 "cannot convert prvalue std2::box<int> to std2::unsafe_cell<std2::box<int>>")

Diff for: libsafecxx/test/compile-fail/box2.cxx

@@ -0,0 +1,13 @@
+// Copyright 2024 Christian Mazakas
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#feature on safety
+
+#include <std2.h>
+
+int main()
+{
+    std2::box<int> p(1234);
+    auto p2 = cpy p;
+}