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// FIXME: Replace `AsciiChar` with `[core:ascii::Char]` once [#110998] is stable
#![allow(unreachable_pub)]
use core::ops::{Deref, Index, IndexMut};
pub use _ascii_char::AsciiChar;
/// A string that only contains ASCII characters, same layout as [`str`].
#[derive(Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct AsciiStr([AsciiChar]);
impl AsciiStr {
#[inline]
pub const fn new_sized<const N: usize>(src: &str) -> [AsciiChar; N] {
if !src.is_ascii() || src.len() > N {
panic!();
}
let src = src.as_bytes();
let mut result = [AsciiChar::NULL; N];
let mut i = 0;
while i < src.len() {
result[i] = AsciiChar::new(src[i]);
i += 1;
}
result
}
#[inline]
pub const fn from_slice(src: &[AsciiChar]) -> &Self {
// SAFETY: `Self` is transparent over `[AsciiChar]`.
unsafe { core::mem::transmute::<&[AsciiChar], &AsciiStr>(src) }
}
#[inline]
pub const fn as_str(&self) -> &str {
// SAFETY: `Self` has the same layout as `str`,
// and all ASCII characters are valid UTF-8 characters.
unsafe { core::mem::transmute::<&AsciiStr, &str>(self) }
}
#[inline]
pub const fn len(&self) -> usize {
self.0.len()
}
#[inline]
pub const fn is_empty(&self) -> bool {
self.0.is_empty()
}
}
// Must not implement `DerefMut`. Not every `char` is an ASCII character.
impl Deref for AsciiStr {
type Target = str;
#[inline]
fn deref(&self) -> &Self::Target {
self.as_str()
}
}
impl<Idx> Index<Idx> for AsciiStr
where
[AsciiChar]: Index<Idx, Output = [AsciiChar]>,
{
type Output = [AsciiChar];
#[inline]
fn index(&self, index: Idx) -> &Self::Output {
&self.0[index]
}
}
impl<Idx> IndexMut<Idx> for AsciiStr
where
[AsciiChar]: IndexMut<Idx, Output = [AsciiChar]>,
{
#[inline]
fn index_mut(&mut self, index: Idx) -> &mut Self::Output {
&mut self.0[index]
}
}
impl Default for &'static AsciiStr {
#[inline]
fn default() -> Self {
// SAFETY: `Self` has the same layout as `str`.
unsafe { core::mem::transmute::<&str, &AsciiStr>("") }
}
}
impl AsciiChar {
pub const NULL: AsciiChar = AsciiChar::new(0);
#[inline]
pub const fn slice_as_bytes<const N: usize>(src: &[AsciiChar; N]) -> &[u8; N] {
// SAFETY: `[AsciiChar]` has the same layout as `[u8]`.
unsafe { core::mem::transmute::<&[AsciiChar; N], &[u8; N]>(src) }
}
#[inline]
pub const fn two_digits(d: u32) -> [Self; 2] {
const ALPHABET: &[u8; 10] = b"0123456789";
if d >= ALPHABET.len().pow(2) as u32 {
panic!();
}
[
Self::new(ALPHABET[d as usize / ALPHABET.len()]),
Self::new(ALPHABET[d as usize % ALPHABET.len()]),
]
}
#[inline]
pub const fn two_hex_digits(d: u32) -> [Self; 2] {
const ALPHABET: &[u8; 16] = b"0123456789abcdef";
if d >= ALPHABET.len().pow(2) as u32 {
panic!();
}
[
Self::new(ALPHABET[d as usize / ALPHABET.len()]),
Self::new(ALPHABET[d as usize % ALPHABET.len()]),
]
}
}
mod _ascii_char {
/// A character that is known to be in ASCII range, same layout as [`u8`].
#[derive(Debug, Clone, Copy, Default, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct AsciiChar(u8);
impl AsciiChar {
#[inline]
pub const fn new(c: u8) -> Self {
if c.is_ascii() { Self(c) } else { panic!() }
}
}
}