>From Nim 1.4 release blog post: Known incompatibilities and gotchas Deepcopy If you use system.deepCopy in your code, you need to enable it via --deepCopy:on on the command line. This is a band-aid and a better solution for this will arrive in the future.
The reason for this opt-in switch is that ARC and ORC do not use the old runtime type information (RTTI) that system.deepCopy is built upon. We’ve built ARC and ORC with embedded devices in mind where the overhead of the old RTTI has been reported to be unacceptable. * <https://nim-lang.org/blog/2020/10/16/version-140-released.html> * <https://github.com/nim-lang/Nim/issues/15405>
