That being said, I can understand why this might not necessarily be desirable for some people; Copy is generally reserved for types that are "small enough" that implicitly copying the bytes will be cheap enough to ignore. It might seem obvious that a struct containing two types that are Copy should also be cheap enough to be Copy, the line has to be drawn _somewhere_, and for any number of bytes that is chosen to be the threshold where the cost is too high, it's pretty easy to pick a size that's below that threshold but a struct containing two instances of that size is above the threshold. Because of the unclear boundaries for that sort of thing, I generally tend only to derive Copy on things in my code that thin wrappers around existing types that are Copy, e.g. `struct Foo(i32)`.
https://github.com/rust-lang/rust/issues/48649#issuecomment-...