# Rust by Example

## 17.2 Vectors

Vectors are re-sizable arrays. Like slices, their size is not known at compile time, but they can grow or shrink at any time. A vector is represented using 3 words: a pointer to the data, its length, and its capacity. The capacity indicates how much memory is reserved for the vector. The vector can grow as long as the length is smaller than the capacity. When this threshold needs to be surpassed, the vector is reallocated with a larger capacity.

fn main() {
// Iterators can be collected into vectors
let collected_iterator: Vec<i32> = (0..10).collect();
println!("Collected (0..10) into: {:?}", collected_iterator);

// The vec! macro can be used to initialize a vector
let mut xs = vec![1i32, 2, 3];
println!("Initial vector: {:?}", xs);

// Insert new element at the end of the vector
println!("Push 4 into the vector");
xs.push(4);
println!("Vector: {:?}", xs);

// Error! Immutable vectors can't grow
collected_iterator.push(0);
// FIXME ^ Comment out this line

// The len method yields the current size of the vector
println!("Vector size: {}", xs.len());

// Indexing is done using the square brackets (indexing starts at 0)
println!("Second element: {}", xs[1]);

// pop removes the last element from the vector and returns it
println!("Pop last element: {:?}", xs.pop());

// Out of bounds indexing yields a panic
println!("Fourth element: {}", xs[3]);
}

More Vec methods can be found under the std::vec module