Vec<T>

Create dynamic arrays with Vec<T>.

Defining a Vec<T>

Vec<T> is a collection that stores values of the same type contiguously and can grow or shrink at runtime. The elements live on the heap; the vector itself (pointer, length, capacity) is on the stack:

let bos: Vec<i32> = Vec::new();   // the type must be given
let sifirlar = vec![0; 4];        // [0, 0, 0, 0]
let sayilar = vec![1, 2, 3];      // type inferred: Vec<i32>

Since an empty vector has no elements, the compiler can't guess the type; either you write it or it's inferred from later use.

Array or vector?

An array ([i32; 3]) has a fixed size and lives on the stack; the size is part of the type. A vector can grow. If the size is known at compile time and won't change, use an array; otherwise a vector:

let aylar = ["Oca", "Şub", "Mar"];      // [&str; 3]
let mut notlar = Vec::new();
notlar.push(85);                         // Vec<i32>

Both convert to a &[T] slice, so functions taking slices work with both.

Exercise Create vectors

Create three vectors: an empty Vec<i32> (Vec::new()), vec![0; 4] and vec![1, 2, 3]. Print the empty vector's length and the other two with {:?} on one line.

Show example solution

fn main() {
    let bos: Vec<i32> = Vec::new();
    let sifirlar = vec![0; 4];
    let sayilar = vec![1, 2, 3];
    println!("{} {:?} {:?}", bos.len(), sifirlar, sayilar);
}

Test yourself

What is <code>vec![7; 3]</code>?
- [3, 3, 3, 3, 3, 3, 3]
- [0, 1, 2]
- [7, 7, 7]
- [7, 3]
Show answer

[7, 7, 7] — vec![value; count] produces the given number of copies of the value.

Repeated vector

let sifirlar = vec![0____4];   // [0, 0, 0, 0]

Show answer

let sifirlar = vec![0;4];   // [0, 0, 0, 0]

Expression and result

Vec::<i32>::new()

[]
vec![0; 4]

[0, 0, 0, 0]
vec![1, 2, 3].len()

3
[1, 2, 3]

Array, fixed size

Next lesson: Push and pop

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