Function itertools::concat

pub fn concat<I>(iterable: I) -> I::Item where
    I: IntoIterator,
    I::Item: Extend<<<I as IntoIterator>::Item as IntoIterator>::Item> + IntoIterator + Default, 

Combine all an iterator’s elements into one element by using Extend.

IntoIterator-enabled version of Itertools::concat.

This combinator will extend the first item with each of the rest of the items of the iterator. If the iterator is empty, the default value of I::Item is returned.

use itertools::concat;
 
let input = vec![vec![1], vec![2, 3], vec![4, 5, 6]];
assert_eq!(concat(input), vec![1, 2, 3, 4, 5, 6]);