Rust by Example

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 length, which is known at compile time, is part of their type signature [T; length].

Slices are similar to arrays, but their length 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. The word size is the same as usize, determined by the processor architecture eg 64 bits on an x86-64. 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 count of elements in the array

println!("number of elements in array: {}", 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

// They are of the form [starting_index..ending_index]

// starting_index is the first position in the slice

// ending_index is one more than the last position in the slice

println!("borrow a section of the array as a slice");

analyze_slice(&ys[1 .. 4]);

// Out of bound indexing causes compile error

println!("{}", xs[5]);

}

הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX