[tialaramex]

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.

[hinkley]

Yeah this is a function called sort_by but I don’t think it’s doing the same thing.

    let (initial_values, stream) = (initial_values, stream)
            .filter(filter)
            .sort_by(new_sorter_lexicographic(vec![
                // Sort by latest event's kind.
                Box::new(new_sorter_latest_event()),
                // Sort rooms by their recency.
                Box::new(new_sorter_recency()),
                // Finally, sort by name.
                Box::new(new_sorter_name()),
            ]))
            .dynamic_head_with_initial_value(page_size, limit_stream);

That’s an api that would make an OG Java developer get tingles.

sortBy should be locking each object once and I’m reasonably sure this is happening at least three times. Author ends up approximating _.sortBy() at the bottom by introducing a struct.