Function chain

pub fn chain<I, J>(
    i: I,
    j: J,
) -> Chain<<I as IntoIterator>::IntoIter, <J as IntoIterator>::IntoIter> 
where
    I: IntoIterator,
    J: IntoIterator<Item = <I as IntoIterator>::Item>,

Create an iterator that first iterates i and then j.

IntoIterator enabled version of i.chain(j).

use itertools::chain;

for elt in chain(&[1, 2, 3], &[4]) {
    /* loop body */
}