Vec

Vec is the standard resizable heap-allocated buffer:

fn main() {
    let mut v1 = Vec::new();
    v1.push(42);
    println!("v1: len = {}, capacity = {}", v1.len(), v1.capacity());
    let mut v2 = Vec::with_capacity(v1.len() + 1);
    v2.extend(v1.iter());
    v2.push(9999);
    println!("v2: len = {}, capacity = {}", v2.len(), v2.capacity());
}
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Vec implements Deref<Target = [T]>, which means that you can call slice methods on a Vec.

Speaker Notes

  • Vec is a type of collection, along with String and HashMap. The data it contains is stored on the heap. This means the amount of data doesnโ€™t need to be known at compile time. It can grow or shrink at runtime.

  • Notice how Vec<T> is a generic type too, but you donโ€™t have to specify T explicitly. As always with Rust type inference, the T was established during the first push call.

  • vec![...] is a canonical macro to use instead of Vec::new() and it supports adding initial elements to the vector.

  • To index the vector you use [ ], but they will panic if out of bounds. Alternatively, using get will return an Option. The pop function will remove the last element.

    println!("v2: len = {}, capacity = {}, {:?}", v2.len(), v2.capacity(), v2.get(0)); println!("{:?}",v2.pop());

  • Show iterating over a vector and mutating the value: for e in &mut v { *e += 50; }