Not necessarily. A new type could be introduced and the old one deprecated.
Even without introducing a new type, it could be improved in a backwards compatible way. For example, derive the Copy trait, and add a contains method that takes an owned value instead of a reference (at least as long as the Idx type is Copy).
> In 2021 edition the compiler team could change the
meaning of (3..5) to resolve to a new type. Then if you wanted
the old type you have to request it by a fully qualified name
or something.
And the responses was:
> That would be pretty awful. I think it would be
better to change IntoIterator and warn for differences
in copy and intoiterator in both editions so you can write portable code.
