reverse vs. rev methods on DoubleEndedIterator are confusing

[thestinger]

The reverse method is an in-place reversal and the rev method flips the direction of iteration. There has to be a better naming scheme for this.

[jfager]

I feel like "reverse" is the odd duck here. It's a little surprising that the way you reverse a collection in-place is via a method on its iterator, it seems like it should be on the collection directly. Meanwhile, rev is exactly what I'd expect.

[thestinger]

It's a little surprising that the way you reverse a collection in-place is via a method on its iterator, it seems like it should be on the collection directly.

I don't understand what you're saying. The reverse method on iterators doesn't reverse a container, it reverses the elements yielded by an iterator in-place:

fn main() {
    let mut xs = [1, 2, 3];
    let mut ys = [4, 5, 6];
    xs.mut_iter().chain(ys.mut_iter()).reverse_();
    println!("{:?} {:?}", xs, ys);
}

Note that the trailing underscore is a workaround for a compiler bug / language design issue. A generic implementation of a trait causes the name to be reserved on all types if the trait is in scope.

[pnkfelix]

see also #10632

[pnkfelix]

I idly wonder whether one way to deal with issues like this would be via a design heuristic such as "if the same concept can be implemented by both an in-place modification of the receiver and a pure operation that constructs a fresh object, then one should use a method for the in-place modification, and a separate function for the construction."

(But this is based on the assumption that people would be less likely to think that a separate function modifies its argument, which may be unfounded.)

[jfager]

The description of reverse_ in the docs is "Use an iterator to reverse a container in-place", and

let mut xs = [1, 2, 3];
xs.mut_iter().reverse_();
println!("{:?}", xs);

does just that, so hopefully you see how someone could be confused.

Anyways, I'm not saying "get rid of reverse", I'm saying that of the two use cases, rev seems far more common and so should have first dibs on the name. reverse could maybe become something like rev_swap?

[nwin]

Why not use .reversed() instead of .rev()? I think .rev() is much too cryptic (could mean revert as in resetting the iterator). Abbreviations are imo ok for such a thing like .iter(), but .rev() will be used muss less often and should be self-descriptive.

[aturon]

This has been addressed with the recent rename to reverse_in_place.