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use core::ops;
/// A specialized copy-on-write byte string.
///
/// The purpose of this type is to permit usage of a "borrowed or owned
/// byte string" in a way that keeps std/no-std compatibility. That is, in
/// no-std mode, this type devolves into a simple &[u8] with no owned variant
/// available. We can't just use a plain Cow because Cow is not in core.
#[derive(Clone, Debug)]
pub struct CowBytes<'a>(Imp<'a>);
// N.B. We don't use std::borrow::Cow here since we can get away with a
// Box<[u8]> for our use case, which is 1/3 smaller than the Vec<u8> that
// a Cow<[u8]> would use.
#[cfg(feature = "std")]
#[derive(Clone, Debug)]
enum Imp<'a> {
Borrowed(&'a [u8]),
Owned(Box<[u8]>),
}
#[cfg(not(feature = "std"))]
#[derive(Clone, Debug)]
struct Imp<'a>(&'a [u8]);
impl<'a> ops::Deref for CowBytes<'a> {
type Target = [u8];
#[inline(always)]
fn deref(&self) -> &[u8] {
self.as_slice()
}
}
impl<'a> CowBytes<'a> {
/// Create a new borrowed CowBytes.
#[inline(always)]
pub fn new<B: ?Sized + AsRef<[u8]>>(bytes: &'a B) -> CowBytes<'a> {
CowBytes(Imp::new(bytes.as_ref()))
}
/// Create a new owned CowBytes.
#[cfg(feature = "std")]
#[inline(always)]
pub fn new_owned(bytes: Box<[u8]>) -> CowBytes<'static> {
CowBytes(Imp::Owned(bytes))
}
/// Return a borrowed byte string, regardless of whether this is an owned
/// or borrowed byte string internally.
#[inline(always)]
pub fn as_slice(&self) -> &[u8] {
self.0.as_slice()
}
/// Return an owned version of this copy-on-write byte string.
///
/// If this is already an owned byte string internally, then this is a
/// no-op. Otherwise, the internal byte string is copied.
#[cfg(feature = "std")]
#[inline(always)]
pub fn into_owned(self) -> CowBytes<'static> {
match self.0 {
Imp::Borrowed(b) => CowBytes::new_owned(Box::from(b)),
Imp::Owned(b) => CowBytes::new_owned(b),
}
}
}
impl<'a> Imp<'a> {
#[cfg(feature = "std")]
#[inline(always)]
pub fn new(bytes: &'a [u8]) -> Imp<'a> {
Imp::Borrowed(bytes)
}
#[cfg(not(feature = "std"))]
#[inline(always)]
pub fn new(bytes: &'a [u8]) -> Imp<'a> {
Imp(bytes)
}
#[cfg(feature = "std")]
#[inline(always)]
pub fn as_slice(&self) -> &[u8] {
match self {
Imp::Owned(ref x) => x,
Imp::Borrowed(x) => x,
}
}
#[cfg(not(feature = "std"))]
#[inline(always)]
pub fn as_slice(&self) -> &[u8] {
self.0
}
}