rust thoughts of an execerise (What do you think is the more commonly used pattern under Rust developers?)

[zzz6519003]

// vecs2.rs
// A Vec of even numbers is given. Your task is to complete the loop
// so that each number in the Vec is multiplied by 2.
//
// Make me pass the test!
//
// Execute `rustlings hint vecs2` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn vec_loop(mut v: Vec<i32>) -> Vec<i32> {
    for i in v.iter_mut() {
        // TODO: Fill this up so that each element in the Vec `v` is
        // multiplied by 2.
        println!("{}",i);
        *i = *i * 2;
    }

    // At this point, `v` should be equal to [4, 8, 12, 16, 20].
    v
}

fn vec_map(v: &Vec<i32>) -> Vec<i32> {
    v.iter().map(|num| {
        // TODO: Do the same thing as above - but instead of mutating the
        // Vec, you can just return the new number!
        num * 2
    }).collect()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_vec_loop() {
        let v: Vec<i32> = (1..).filter(|x| x % 2 == 0).take(5).collect();
        let ans = vec_loop(v.clone());

        assert_eq!(ans, v.iter().map(|x| x * 2).collect::<Vec<i32>>());
    }

    #[test]
    fn test_vec_map() {
        let v: Vec<i32> = (1..).filter(|x| x % 2 == 0).take(5).collect();
        let ans = vec_map(&v);

        assert_eq!(ans, v.iter().map(|x| x * 2).collect::<Vec<i32>>());
    }
}

[zzz6519003]

hint
Hint 1: i is each element from the Vec as they are being iterated. Can you try
multiplying this?

Hint 2: For the first function, there's a way to directly access the numbers stored
in the Vec, using the * dereference operator. You can both access and write to the
number that way.

After you've completed both functions, decide for yourself which approach you like
better. What do you think is the more commonly used pattern under Rust developers?

[zzz6519003]

second question:

hint
So, vec0 is passed into the fill_vec function as an argument. In Rust,
when an argument is passed to a function and it's not explicitly returned,
you can't use the original variable anymore. We call this "moving" a variable.
Variables that are moved into a function (or block scope) and aren't explicitly
returned get "dropped" at the end of that function. This is also what happens here.
There's a few ways to fix this, try them all if you want:

1. Make another, separate version of the data that's in vec0 and pass that
   to fill_vec instead.
2. Make fill_vec borrow its argument instead of taking ownership of it,
   and then copy the data within the function in order to return an owned
   Vec<i32>
3. Make fill_vec mutably borrow a reference to its argument (which will need to be
   mutable), modify it directly, then not return anything. Then you can get rid
   of vec1 entirely -- note that this will change what gets printed by the
   first println!