Rust by Example

25 Arrays and Slices

An array is a collection of objects of the same type T, stored in contiguous memory. Arrays are created using brackets [], and their size, which is known at compile time, is part of their type signature [T; size].

Slices are similar to arrays, but their size is not known at compile time. Instead, a slice is a two-word object, the first word is a pointer to the data, and the second word is the length of the slice. Slices can be used to borrow a section of an array, and have the type signature &[T].

use std::mem; // This function borrows a slice fn analyze_slice(slice: &[i32]) { println!("first element of the slice: {}", slice[0]); println!("the slice has {} elements", slice.len()); } fn main() { // Fixed-size array (type signature is superfluous) let xs: [i32; 5] = [1, 2, 3, 4, 5]; // All elements can be initialized to the same value let ys: [i32; 500] = [0; 500]; // Indexing starts at 0 println!("first element of the array: {}", xs[0]); println!("second element of the array: {}", xs[1]); // `len` returns the size of the array println!("array size: {}", xs.len()); // Arrays are stack allocated println!("array occupies {} bytes", mem::size_of_val(&xs)); // Arrays can be automatically borrowed as slices println!("borrow the whole array as a slice"); analyze_slice(&xs); // Slices can point to a section of an array println!("borrow a section of the array as a slice"); analyze_slice(&ys[1 .. 4]); // Out of bound indexing yields a panic println!("{}", xs[5]); }