That's a good point and I think I will add a paragraph or too about that. The simplest answer is: as long as you're not doing any unsafe Rust you should just us

That's a good point and I think I will add a paragraph or too about that. The simplest answer is: as long as you're not doing any unsafe Rust you should just use whatever is derived from types within a type. If you have a struct where all fields are `Send`, then the struct will be `Send` too. If you add anything that is `!Send` (like `Cell`), it will be `!Send` and you don't have to explicitly mark is as `!Send`. The most common exception to this is when you implement a type that has a `!Send` attribute, but you still mark it as `Send`, because you implement an API that guards against misusing the type. I honestly can't think of any practical example of the opposite (ie. you have a type with all `Send` attributes), but that would probably be similar: you have a type with all `Send` attributes, but you implement some kind of API that makes it unsafe to sent the type between threads.