Vec<T>
- Rust course
- Beginner
- Lesson 94/115
- 4 min
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.
Practice 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.
Starter code
fn main() {
// buraya yaz
}Sample 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);
}Expected output
0 [0, 0, 0, 0] [1, 2, 3]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is <code>vec![7; 3]</code>?
- [3, 3, 3, 3, 3, 3, 3]
- [0, 1, 2]
- [7, 7, 7] Correct answer
- [7, 3]
Explanation: vec![value; count] produces the given number of copies of the value.
2 Repeated vector
let sifirlar = vec![0____4]; // [0, 0, 0, 0]let sifirlar = vec![0;4]; // [0, 0, 0, 0]Explanation: In the vec![value; count] syntax, the separator is a semicolon.
3 Expression and result
| Term | Meaning |
|---|---|
Vec::<i32>::new() |
[] |
vec![0; 4] |
[0, 0, 0, 0] |
vec![1, 2, 3].len() |
3 |
[1, 2, 3] |
Array, fixed size |