Rust's slice of T [T] provides [T]::sort_by_cached_key which is a stable IPN sort which lets you provide a key transform callable f, which it will call at most once for each item to be sorted, sorting by comparing the (cached) results from that callable.

https://doc.rust-lang.org/std/primitive.slice.html#method.so...

However ..._by_cached_key is not provided for Rust's unstable sort because the unstable sort doesn't require an allocator and necessarily a cache does need an allocator.