While interesting, this entire article works with a static MyStruct. This means the type already is Any, and if you define MyTrait: 'static, then you can do the downcast by first casting to an Arc<dyn Any> and using one of the downcast methods.

For non-'static types, downcasting soundly is incredibly difficult. You need to somehow get the correct lifetime back from the trait. You're better off using unsafe at that point anyway. If the trait itself holds the lifetime (impl<'a> MyTrait<'a> for MyStruct<'a>), then that can help with it, though I'm not really sure how lifetime variance plays into the soundness of a downcast here.

Finally, at the end, I'd rather just use an assert! over an unchecked assertion. I know the goal is to look at the assembly with that assertion in place, so it makes sense why they used it here. In practice, an actual assertion is a lot better because the compiler gets the same information from it and you get validation at runtime that the information is correct.

Anyway, great article! The goal was to explore how Arc casting works, and I think it does a great job at showing and explaining that.