#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(ascii_char)]
const HEX_DIGITS: [std::ascii::Char; 16] = *b"0123456789abcdef".as_ascii().unwrap();
fn main() {
    assert_eq!(HEX_DIGITS[1].as_str(), "1");
    assert_eq!(HEX_DIGITS[10].as_str(), "a");
}