Add in Rust 1.55

To add an element to an array in Rust 1.55, we need to first create an array with a fixed size and then use the std::mem::replace() function from the Rust standard library to replace an element at a specific index with a new value.

Here's an example code snippet that shows how to add an element to an array:

fn main() {
    // Create a fixed-size array with 3 elements
    let mut arr = [1, 2, 3];
// Use std::mem::replace() to replace an element at index 2 with a new value

    arr = {

        let mut temp = std::mem::replace(&mut arr, [0; 4]);

        temp[2] = 4;

        temp

    };
// Print the updated array

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

}

In this example, we first create an array arr with three elements [1, 2, 3]. Then, we use std::mem::replace() to replace the array arr with a new array of size 4 [0; 4], where all elements are initialized to 0. We store the old array in a mutable variable named temp.

Next, we update the element at index 2 of temp to 4. Finally, we return temp with the updated element and assign it back to arr. Now, arr has a new element [1, 2, 4, 0].

Output:

[1, 2, 4, 0]