> The type system can't know whether you call `T::clone()` in a method somewhere. It’s not about that, it’s about type system power as the article said. In for

> The type system can't know whether you call `T::clone()` in a method somewhere. 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=d1947d81a126df84f3c91fb29b5d5efc https://play.rust-lang.org/?gist=d1947d81a126df84f3c91fb29b5...>: impl<T> Clone for WrapArc<T> where Arc<T>: Clone, { … }