I believe this is referring to '...and keep a mutable reference to it' ie. A singleton, and many overseer style observe-and-update-on-change data binding patte

I believe this is referring to '...and keep a mutable reference to it' ie. A singleton, and many overseer style observe-and-update-on-change data binding patterns. Basically, shared ownership is pretty central to many C++ patterns, which means they translate poorly into rust.