Collections

Vectors

To store expandable list of same type of elements, use vec

let elements: Vec<i32> = Vec::new();

Vectors only store same types of elements

Consider below code

let mut v = vec![1, 3, 4];
let first_element = &v[0]; // immutable borrow

v.push(7); //error //mutable

println!("{}", first_element); //immable borrow value accessing

Error occurs at line 4. Because we are doing a mutable borrow after immutably referencing the value at line 2. Even though it's a reference, there will still be error because internally, Rust might deallocate memory and allocate to a new memory. If this happens first_element might be referencing to deallocated memory.

To store different kind of elements inside vector, then use enums!

fn store_different_elements() {
    let mut diff_value_vec = vec![Store::IntValue(2), 
                                Store::StringValue(String::from("Helo"))];
    diff_value_vec.push(Store::IntValue(9));
    //diff_value_vec.push(10);
}

enum Store {
    IntValue(u32),
    StringValue(String),
}

Rust needs to know what kind of values are stored inside vector at compile time so that it would know how memory is needed for allocation in the heap