Same! =D

You don't have flatten, but you can easily replace it with flat_map:

let a = [vec![1, 3, 5], vec![7, 9]];
// let flat = a.iter().flatten().collect::<Vec<_>>();
let flat = a.iter().flat_map(|x| x).collect::<Vec<_>>();
println!("{:?}", flat);

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