[mbrubeck]

It's possible in Rust too, but only for a subset of element types: those that support shared mutation (also known as "internal mutation"). For example, a type containing an `AtomicU32` or a `Mutex<T>` or a `Cell<T>` could have an `Ord::cmp` implementation that alters its value, and the compiler will not prevent this.

[orlp]

Yes, I had a nasty bug in an initial version of glidesort where I (naively) assumed that I could create a temporary copy of an element by doing a memcpy and call the comparison function on this temporary copy a bunch of times before throwing it away, since I assumed the comparison function would not mutate the copy. Unfortunately interior mutability means this would lead to potential double drops, and it was just not sound.