How do I initialize an array of vectors?

Question

I would like to create an array of vectors:

fn main() {     let v: [Vec<u8>; 10] = [Vec::new(); 10]; } 

However, the compiler gives me this error:

error[E0277]: the trait bound `std::vec::Vec<u8>: std::marker::Copy` is not satisfied  --> src/main.rs:2:28   | 2 |     let v: [Vec<u8>; 10] = [Vec::new(); 10];   |                            ^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `std::vec::Vec<u8>`   |   = note: the `Copy` trait is required because the repeated element will be copied 

Answer 1

You cannot use the [expr; N] initialisation syntax for non-Copy types because of Rust’s ownership model—it executes the expression once only, and for non-Copy types it cannot just copy the bytes N times, they must be owned in one place only.

You will need to either:

1. Write it out explicitly ten times: let v: [Vec<u8>; 10] = [vec![], vec![], vec![], vec![], vec![], vec![], vec![], vec![], vec![], vec![]], or

2. Use something like a vector instead of the array: std::iter::repeat(vec![]).take(10).collect::<Vec<_>>().

See also:

• Initialize a large, fixed-size array with non-Copy types