1use crate::mem::MaybeUninit;
2use crate::{fmt, str};
3
4/// Used for slow path in `Display` implementations when alignment is required.
5pub(super) struct DisplayBuffer<const SIZE: usize> {
6 buf: [MaybeUninit<u8>; SIZE],
7 len: usize,
8}
9
10impl<const SIZE: usize> DisplayBuffer<SIZE> {
11 #[inline]
12 pub(super) const fn new() -> Self {
13 Self { buf: [MaybeUninit::uninit(); SIZE], len: 0 }
14 }
15
16 #[inline]
17 pub(super) fn as_str(&self) -> &str {
18 // SAFETY: `buf` is only written to by the `fmt::Write::write_str` implementation
19 // which writes a valid UTF-8 string to `buf` and correctly sets `len`.
20 unsafe {
21 let s: &[u8] = self.buf[..self.len].assume_init_ref();
22 str::from_utf8_unchecked(s)
23 }
24 }
25}
26
27impl<const SIZE: usize> fmt::Write for DisplayBuffer<SIZE> {
28 fn write_str(&mut self, s: &str) -> fmt::Result {
29 let bytes: &[u8] = s.as_bytes();
30
31 if let Some(buf: &mut [MaybeUninit]) = self.buf.get_mut(self.len..(self.len + bytes.len())) {
32 buf.write_copy_of_slice(src:bytes);
33 self.len += bytes.len();
34 Ok(())
35 } else {
36 Err(fmt::Error)
37 }
38 }
39}
40