[proto_lambda]

It's definitely not a data structure that makes the borrow checker happy. Luckily it's also not a data structure that's required or desirable in 99% of cases, but the standard library still offers an implementation for those 1% so people don't try to write their own (turns out getting a doubly linked list correct isn't quite as trivial as it may seem).

[Waterluvian]

I’m actually a bit surprised it’s in the standard library if it’s so uncommonly needed. Isn’t Rust’s stdlib tiny with a philosophy of letting the community fill in most things?

[estebank]

There were arguments made for its non-inclusion[1].

[1]: https://rust-unofficial.github.io/too-many-lists/sixth.html

[Waterluvian]

I enjoyed reading this. A fun style.