Comment by chrismorgan

It’s not about that, it’s about type system power as the article said. In former days there was no way to express the constraint; but these days you can <https://play.rust-lang.org/?gist=d1947d81a126df84f3c91fb29b5...>:

  impl<T> Clone for WrapArc<T>
  where
      Arc<T>: Clone,
  {
      …
  }