HN user
You're getting a lot of pushback in the comments here and I don't understand why. This is exactly right. Stay consistent with the existing way or commit to changing it all (not necessary all at once) so it's consistent again, but better.
How is it a subset then if it has the @-prefix? Wait, does Rust's grammar still have the @ and ~ sigils from the pre 1.0 times for pointers?
All of them do.
There is a collection of benchmarks of the fastest sudoku solvers here: https://github.com/t-dillon/tdoku/tree/master/benchmarks
How fast they are depends on the difficulty of the sudoku and on your machine, but it's typically a few thousand/s on the hardest known and several 100k/s to a million/s on very easy.