How to get a slice as an array in Rust?

I have an array of an unknown size, and I would like to get a slice of that array and convert it to a statically sized array:

fn pop(barry: &[u8]) -> [u8; 3] {
    barry[0..3] // expected array `[u8; 3]`, found slice `[u8]`
}

How would I do this?

You can easily do this with the TryInto trait (which was stabilized in Rust 1.34):
// Before Rust 2021, you need to import the trait:
// use std::convert::TryInto;

fn pop(barry: &[u8]) -> [u8; 3] {
barry.try_into().expect("slice should have length 3")
}


But even better: there is no need to clone/copy your elements! It is actually possible to get a &[u8; 3] from a &[u8]:
fn pop(barry: &[u8]) -> &[u8; 3] {
barry.try_into().expect("slice should have length 3")
}


As mentioned in the other answers, you probably don't want to panic if the length of barry is not 3, but instead handle this error gracefully.

This works thanks to these impls of the related trait TryFrom (before Rust 1.47, these only existed for arrays up to length 32):
impl TryFrom for [T; N]
where
T: Copy,

impl TryFrom for &'a [T; N]

impl TryFrom for &'a mut [T; N]


Stack Overflow Q#25428920, score: 203