Function itertools::enumerate

Important traits for Enumerate<I>

impl<I> Iterator for Enumerate<I> where
    I: Iterator,  type Item = (usize, <I as Iterator>::Item);

pub fn enumerate<I>(iterable: I) -> Enumerate<I::IntoIter> where
    I: IntoIterator, 

Iterate iterable with a running index.

IntoIterator enabled version of .enumerate().

use itertools::enumerate;

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