closures

I am getting an error inside a nested lambda. let rows = vec![ vec![3, 6, 2, 8, 9, 0], vec![0, 0, 1, 4, 5, 1], ]; let pair_sums = rows.iter() .flat_map(|row| { (0 ..= row.len()).map(|i| row[i] + row[i + 1]) }) .collect::<Vec<_>>(); println!("{:?}", pair_sums); error[E0597]: `row` does not live long enough --> src/main.rs:9:40 | 9 | (0..row.len() - 1).map(|i| row[i] + row[i + 1]) | --- ^^^ does not live long enough | | | capture occurs here 10 | }) | - borrowed value only lives until here 11 | .collect::<Vec<_>>(); | - borrowed value needs to live until here I can sort of see why this is

I stumbled across this article and found it very interesting, so I ran some tests on my own: Test One: List<Action> actions = new List<Action>(); for (int i = 0; i < 5; ++i) actions.Add(() => Console.WriteLine(i)); foreach (Action action in actions) action(); Outputs: 5 5 5 5 5 Test Two: List<Action> actions = new List<Action>(); for (int i = 0; i < 5; ++i) { int j = i; actions.Add(() => Console.WriteLine(j)); } foreach (Action action in actions) action(); Outputs: 0 1 2 3 4 According to the article, in Test One all of the lambdas contain a reference to i which causes them to all output 5.

This question already has answers here : Closed 7 years ago . Possible Duplicate: Javascript closure inside loops - simple practical example Seen many posts talking about setTimeout and closures but I'm still not able to pass in a simple for loop counter. for (i = 0; i < 5; i++) { setTimeout(function () { console.log(i); }, Math.floor(Math.random() * 1000)); } Gives 5 5 5 5 5 Would like to have 0 1 2 3 4 What's wrong ? Please don't flame, I thought I have understood the setTimeout() tale but apparently not. You can use a closure to keep a reference to the current value of i within the loop: