[parley]

This does seem very interesting, at first glance. One thought:

> These “scoped life-time” reference counts are used by the C++ shared_ptr⟨T⟩(calling the destructor at the end of the scope), Rust’s Rc⟨T⟩(using the Drop trait), and Nim (using a finally block to call destroy)

So Rust's non-lexical lifetimes doesn't remedy this? Meaning the actual drop of xs needing to occur at the end of the example in the beginning of section 2.2, as opposed to right after the map. I would have thought that ys borrows nothing from xs, and the drop can be inserted right after map? Perhaps it's too early in the morning for thinking for me.

[sanxiyn]

No, Rust's non-lexical lifetime does not change when things are dropped at all. It is purely a compile time feature with no run time effects.