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    pub(crate) fn new_owned(
47        bytes: alloc::boxed::Box<[u8]>,
48    ) -> CowBytes<'static> {
49        CowBytes(Imp::Owned(bytes))
50    }
51
52    /// Return a borrowed byte string, regardless of whether this is an owned
53    /// or borrowed byte string internally.
54    #[inline(always)]
55    pub(crate) fn as_slice(&self) -> &[u8] {
56        self.0.as_slice()
57    }
58
59    /// Return an owned version of this copy-on-write byte string.
60    ///
61    /// If this is already an owned byte string internally, then this is a
62    /// no-op. Otherwise, the internal byte string is copied.
63    #[cfg(feature = "alloc")]
64    #[inline(always)]
65    pub(crate) fn into_owned(self) -> CowBytes<'static> {
66        match self.0 {
67            Imp::Borrowed(b) => {
68                CowBytes::new_owned(alloc::boxed::Box::from(b))
69            }
70            Imp::Owned(b) => CowBytes::new_owned(b),
71        }
72    }
73}
74
75impl<'a> Imp<'a> {
76    #[inline(always)]
77    pub fn new(bytes: &'a [u8]) -> Imp<'a> {
78        #[cfg(feature = "alloc")]
79        {
80            Imp::Borrowed(bytes)
81        }
82        #[cfg(not(feature = "alloc"))]
83        {
84            Imp(bytes)
85        }
86    }
87
88    #[cfg(feature = "alloc")]
89    #[inline(always)]
90    pub fn as_slice(&self) -> &[u8] {
91        #[cfg(feature = "alloc")]
92        {
93            match self {
94                Imp::Owned(ref x) => x,
95                Imp::Borrowed(x) => x,
96            }
97        }
98        #[cfg(not(feature = "alloc"))]
99        {
100            self.0
101        }
102    }
103
104    #[cfg(not(feature = "alloc"))]
105    #[inline(always)]
106    pub fn as_slice(&self) -> &[u8] {
107        self.0
108    }
109}
memchr/cow.rs

memchr/
cow.rs
