3 A ‘vector’ is a dynamic or ‘growable’ array, implemented as the standard
4 library type [`Vec<T>`][vec]. The `T` means that we can have vectors
5 of any type (see the chapter on [generics][generic] for more).
6 Vectors always allocate their data on the heap.
7 You can create them with the `vec!` macro:
10 let v = vec![1, 2, 3, 4, 5]; // v: Vec<i32>
13 (Notice that unlike the `println!` macro we’ve used in the past, we use square
14 brackets `[]` with `vec!` macro. Rust allows you to use either in either situation,
15 this is just convention.)
17 There’s an alternate form of `vec!` for repeating an initial value:
20 let v = vec![0; 10]; // ten zeroes
25 To get the value at a particular index in the vector, we use `[]`s:
28 let v = vec![1, 2, 3, 4, 5];
30 println!("The third element of v is {}", v[2]);
33 The indices count from `0`, so the third element is `v[2]`.
35 It’s also important to note that you must index with the `usize` type:
38 let v = vec![1, 2, 3, 4, 5];
50 Indexing with a non-`usize` type gives an error that looks like this:
53 error: the trait `core::ops::Index<i32>` is not implemented for the type
54 `collections::vec::Vec<_>` [E0277]
57 note: the type `collections::vec::Vec<_>` cannot be indexed by `i32`
58 error: aborting due to previous error
61 There’s a lot of punctuation in that message, but the core of it makes sense:
62 you cannot index with an `i32`.
64 ## Out-of-bounds Access
66 If you try to access an index that doesn’t exist:
69 let v = vec![1, 2, 3];
70 println!("Item 7 is {}", v[7]);
73 then the current thread will [panic] with a message like this:
76 thread '<main>' panicked at 'index out of bounds: the len is 3 but the index is 7'
79 If you want to handle out-of-bounds errors without panicking, you can use
80 methods like [`get`][get] or [`get_mut`][get_mut] that return `None` when
81 given an invalid index:
84 let v = vec![1, 2, 3];
86 Some(x) => println!("Item 7 is {}", x),
87 None => println!("Sorry, this vector is too short.")
93 Once you have a vector, you can iterate through its elements with `for`. There
97 let mut v = vec![1, 2, 3, 4, 5];
100 println!("A reference to {}", i);
104 println!("A mutable reference to {}", i);
108 println!("Take ownership of the vector and its element {}", i);
112 Vectors have many more useful methods, which you can read about in [their
113 API documentation][vec].
115 [vec]: ../std/vec/index.html
116 [generic]: generics.html
117 [panic]: concurrency.html#panics
118 [get]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get
119 [get_mut]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get_mut