You mean have `byLineCopy` return a `RefCounted!(ByLineCopyImpl, ...)` instance? I suppose it might be OK, but when I added the ref-counting for `ByLine` @monarchdodra preferred that I didn't use `alias this`, and instead added individual forwarding for each method - this avoids exposing any implementation details (such as internal types). Having `ByLineCopy` as a separate `struct` follows the same principle. I don't really mind either way.