Array, vecs

Suppose we want to store a vector in each element of an array. We must first initialize this array, which can be confusing in Rust.

When initializing arrays, each initial element must be a constant. In Rust we can use a const empty array to satisfy this condition.

Example code

In this example program, we create an array of 10 vectors. Each vector is separate, and represents a separate region of memory.

fn main() {
    // Specify an empty vector as a constant.
    const EMPTY: Vec<i32> = vec![];

    // Initialize the array.
    let mut array = [EMPTY; 10];

    // Loop over the array vectors and push 3 numbers to each one.
    for array in array.iter_mut() {
        array.push(1);
        array.push(2);
        array.push(3);
    }

    // Print the vector data in the array.
    for array in array.iter() {
        println!("{:?}", array);
    }
}
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]

A summary

To create an array of vectors, we must initialize with a constant empty array. This allows the array creation expression to compile correctly.