1# Vectors
2
3Vectors are re-sizable arrays. Like slices, their size is not known at compile
4time, but they can grow or shrink at any time. A vector is represented using
53 parameters:
6- pointer to the data
7- length
8- capacity
9
10The capacity indicates how much memory is reserved for the vector. The vector
11can grow as long as the length is smaller than the capacity. When this threshold
12needs to be surpassed, the vector is reallocated with a larger capacity.
13
14```rust,editable,ignore,mdbook-runnable
15fn main() {
16    // Iterators can be collected into vectors
17    let collected_iterator: Vec<i32> = (0..10).collect();
18    println!("Collected (0..10) into: {:?}", collected_iterator);
19
20    // The `vec!` macro can be used to initialize a vector
21    let mut xs = vec![1i32, 2, 3];
22    println!("Initial vector: {:?}", xs);
23
24    // Insert new element at the end of the vector
25    println!("Push 4 into the vector");
26    xs.push(4);
27    println!("Vector: {:?}", xs);
28
29    // Error! Immutable vectors can't grow
30    collected_iterator.push(0);
31    // FIXME ^ Comment out this line
32
33    // The `len` method yields the number of elements currently stored in a vector
34    println!("Vector length: {}", xs.len());
35
36    // Indexing is done using the square brackets (indexing starts at 0)
37    println!("Second element: {}", xs[1]);
38
39    // `pop` removes the last element from the vector and returns it
40    println!("Pop last element: {:?}", xs.pop());
41
42    // Out of bounds indexing yields a panic
43    println!("Fourth element: {}", xs[3]);
44    // FIXME ^ Comment out this line
45
46    // `Vector`s can be easily iterated over
47    println!("Contents of xs:");
48    for x in xs.iter() {
49        println!("> {}", x);
50    }
51
52    // A `Vector` can also be iterated over while the iteration
53    // count is enumerated in a separate variable (`i`)
54    for (i, x) in xs.iter().enumerate() {
55        println!("In position {} we have value {}", i, x);
56    }
57
58    // Thanks to `iter_mut`, mutable `Vector`s can also be iterated
59    // over in a way that allows modifying each value
60    for x in xs.iter_mut() {
61        *x *= 3;
62    }
63    println!("Updated vector: {:?}", xs);
64}
65```
66
67More `Vec` methods can be found under the
68[std::vec][vec] module
69
70[vec]: https://doc.rust-lang.org/std/vec/
71