memchr/
cow.rs

1use core::ops;
2
3/// A specialized copy-on-write byte string.
4///
5/// The purpose of this type is to permit usage of a "borrowed or owned
6/// byte string" in a way that keeps std/no-std compatibility. That is, in
7/// no-std/alloc mode, this type devolves into a simple &[u8] with no owned
8/// variant available. We can't just use a plain Cow because Cow is not in
9/// core.
10#[derive(Clone, Debug)]
11pub struct CowBytes<'a>(Imp<'a>);
12
13// N.B. We don't use alloc::borrow::Cow here since we can get away with a
14// Box<[u8]> for our use case, which is 1/3 smaller than the Vec<u8> that
15// a Cow<[u8]> would use.
16#[cfg(feature = "alloc")]
17#[derive(Clone, Debug)]
18enum Imp<'a> {
19    Borrowed(&'a [u8]),
20    Owned(alloc::boxed::Box<[u8]>),
21}
22
23#[cfg(not(feature = "alloc"))]
24#[derive(Clone, Debug)]
25struct Imp<'a>(&'a [u8]);
26
27impl<'a> ops::Deref for CowBytes<'a> {
28    type Target = [u8];
29
30    #[inline(always)]
31    fn deref(&self) -> &[u8] {
32        self.as_slice()
33    }
34}
35
36impl<'a> CowBytes<'a> {
37    /// Create a new borrowed CowBytes.
38    #[inline(always)]
39    pub(crate) fn new<B: ?Sized + AsRef<[u8]>>(bytes: &'a B) -> CowBytes<'a> {
40        CowBytes(Imp::new(bytes.as_ref()))
41    }
42
43    /// Create a new owned CowBytes.
44    #[cfg(feature = "alloc")]
45    #[inline(always)]
46    fn new_owned(bytes: alloc::boxed::Box<[u8]>) -> CowBytes<'static> {
47        CowBytes(Imp::Owned(bytes))
48    }
49
50    /// Return a borrowed byte string, regardless of whether this is an owned
51    /// or borrowed byte string internally.
52    #[inline(always)]
53    pub(crate) fn as_slice(&self) -> &[u8] {
54        self.0.as_slice()
55    }
56
57    /// Return an owned version of this copy-on-write byte string.
58    ///
59    /// If this is already an owned byte string internally, then this is a
60    /// no-op. Otherwise, the internal byte string is copied.
61    #[cfg(feature = "alloc")]
62    #[inline(always)]
63    pub(crate) fn into_owned(self) -> CowBytes<'static> {
64        match self.0 {
65            Imp::Borrowed(b) => {
66                CowBytes::new_owned(alloc::boxed::Box::from(b))
67            }
68            Imp::Owned(b) => CowBytes::new_owned(b),
69        }
70    }
71}
72
73impl<'a> Imp<'a> {
74    #[inline(always)]
75    pub fn new(bytes: &'a [u8]) -> Imp<'a> {
76        #[cfg(feature = "alloc")]
77        {
78            Imp::Borrowed(bytes)
79        }
80        #[cfg(not(feature = "alloc"))]
81        {
82            Imp(bytes)
83        }
84    }
85
86    #[cfg(feature = "alloc")]
87    #[inline(always)]
88    pub fn as_slice(&self) -> &[u8] {
89        #[cfg(feature = "alloc")]
90        {
91            match self {
92                Imp::Owned(ref x) => x,
93                Imp::Borrowed(x) => x,
94            }
95        }
96        #[cfg(not(feature = "alloc"))]
97        {
98            self.0
99        }
100    }
101
102    #[cfg(not(feature = "alloc"))]
103    #[inline(always)]
104    pub fn as_slice(&self) -> &[u8] {
105        self.0
106    }
107}
memchr/cow.rs

memchr/
cow.rs
