Is there a range expression that can be used to refer to the last N elements of a slice?

Question

I have a slice of unknown length and I would like to try get a slice to the last N elements of that slice. The only way I can think of doing this is as follows (e.g., for 4 elements):

if let [.., a, b, c, d] = my_slice {
    //...
}

This feels very cumbersome though. I would have thought that one of the range expressions would have provided this functionality, but none of them seem to do so... Is there another way of doing this? Ideally, I would be able to work with a slice and not the individual values a, b, c, d in my example above.

user_255688 · Answer

I like your solution, but you could use get. A simple version looks like this:

fn last4(slc: &[T]) -> Option<&[T]> {
    slc.get(slc.len()-4..slc.len())
}

In practice, you'd need to check that slc.len() is at least 4.

See it in action: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=2c9472aea45cf23b1f46b54de7132cd7.

Is there a range expression that can be used to refer to the last N elements of a slice?

1 Answers