Resizing

We said that Vec is a "growable" vector type, but what does that mean? What happens if you try to insert an element into a Vec that's already at maximum capacity?

#![allow(unused)]
fn main() {
let mut numbers = Vec::with_capacity(3);
numbers.push(1);
numbers.push(2);
numbers.push(3); // Max capacity reached
numbers.push(4); // What happens here?
}

The Vec will resize itself.
It will ask the allocator for a new (larger) chunk of heap memory, copy the elements over, and deallocate the old memory.

This operation can be expensive, as it involves a new memory allocation and copying all existing elements.

Vec::with_capacity

If you have a rough idea of how many elements you'll store in a Vec, you can use the Vec::with_capacity method to pre-allocate enough memory upfront.
This can avoid a new allocation when the Vec grows, but it may waste memory if you overestimate actual usage.

Evaluate on a case-by-case basis.

Exercise

The exercise for this section is located in 06_ticket_management/03_resizing