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How can I solve "use of moved value" and "which does not implement the `Copy` trait"?

Tags:

rust

I'm trying to read the values from a vector and use the values as indexes to perform an addition:

fn main() {
    let objetive = 3126.59;

    // 27
    let values: Vec<f64> = vec![
        2817.42, 2162.17, 3756.57, 2817.42, -2817.42, 946.9, 2817.42, 964.42, 795.43, 3756.57,
        139.34, 903.58, -3756.57, 939.14, 828.04, 1120.04, 604.03, 3354.74, 2748.06, 1470.8,
        4695.71, 71.11, 2391.48, 331.29, 1214.69, 863.52, 7810.01,
    ];

    let values_number = values.len();
    let values_index_max = values_number - 1;

    let mut additions: Vec<usize> = vec![0];

    println!("{:?}", values_number);

    while additions.len() > 0 {
        let mut addition: f64 = 0.0;
        let mut saltar: i32 = 0;

        // Sumar valores en additions
        for element_index in additions {
            let addition_aux = values[element_index];
            addition = addition_aux + addition;
        }
    }
}

I get the following error. How can I solve it?

error[E0382]: use of moved value: `additions`
  --> src/main.rs:18:11
   |
18 |     while additions.len() > 0 {
   |           ^^^^^^^^^ value used here after move
...
23 |         for element_index in additions {
   |                              --------- value moved here
   |
   = note: move occurs because `additions` has type `std::vec::Vec<usize>`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `additions`
  --> src/main.rs:23:30
   |
23 |         for element_index in additions {
   |                              ^^^^^^^^^ value moved here in previous iteration of loop
   |
   = note: move occurs because `additions` has type `std::vec::Vec<usize>`, which does not implement the `Copy` trait
like image 998
fontar Avatar asked Mar 15 '18 21:03

fontar


1 Answers

The fix for this particular problem is to borrow the Vec you're iterating over instead of moving it:

for element_index in &additions {
    let addition_aux = values[*element_index];
    addition = addition_aux + addition;
}

but your code has other problems. You never change additions by adding or removing elements, so your while additions.len() > 0 will never terminate. I hope this is because you haven't finished and wanted to work out how to fix the immediate problem before writing the rest of the function.

For now, you might benefit from re-reading the chapter of the Rust Book about ownership, moves, and borrowing.

like image 148
Dan Hulme Avatar answered Nov 01 '22 10:11

Dan Hulme