IteratorExt::rev should be bounded by DoubleEndedIterator

[crumblingstatue]

fn main() {
    (0..10).step_by(2).rev().next();
}

produces the following error:

error: type `core::iter::Rev<core::iter::StepBy<_, core::ops::Range<_>>>` does not implement any method in scope named `next`

According to @eddyb, IteratorExt::rev should be bounded by DoubleEndedIterator to prevent this.

EDIT: Updated the example to show the correct error.

[eddyb]

That's not the problematic error, this is:

error: type `core::iter::Rev<core::iter::StepBy<_, core::ops::Range<_>>>` does not implement any method in scope named `next`
(0..10).step_by(2).rev().next();
                         ^~~~~~

[steveklabnik]

This is basically the same as #23588

[crumblingstatue]

This is basically the same as #23588

They are two different issues. Bounding IteratorExt::rev by DoubleEndedIterator won't make using rev() on the result of step_by() possible.

[steveklabnik]

Yeah, just noting the link :)