This Rust crate provides EternalIterator trait, which promises that the iterator iterates forever.
rs
let mut it = core::iter::repeat(123_i32).map(|i| i * 2)
.enumerate().skip(5).step_by(2).zip(core::iter::once(3).chain(10..));
assert_eq!(it.next_eternal(), ((5, 246), 3));
assert_eq!(it.next_eternal(), ((7, 246), 10));
assert_eq!(it.next(), Some(((9, 246), 11)));
assert_eq!(it.next_eternal(), ((11, 246), 12));