bendns' repos / rust-analyzer
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Diffstat
-rw-r--r--lib/smol_str/README.md3
-rw-r--r--lib/smol_str/src/lib.rs39
2 files changed, 26 insertions, 16 deletions
diff --git a/lib/smol_str/README.md b/lib/smol_str/README.md
index 5e3506846f..ce16759e81 100644
--- a/lib/smol_str/README.md
+++ b/lib/smol_str/README.md
@@ -7,13 +7,14 @@
A `SmolStr` is a string type that has the following properties:
-* `size_of::<SmolStr>() == 24 (therefore == size_of::<String>() on 64 bit platforms)
+* `size_of::<SmolStr>() == 24` (therefore `== size_of::<String>()` on 64 bit platforms)
* `Clone` is `O(1)`
* Strings are stack-allocated if they are:
* Up to 23 bytes long
* Longer than 23 bytes, but substrings of `WS` (see `src/lib.rs`). Such strings consist
solely of consecutive newlines, followed by consecutive spaces
* If a string does not satisfy the aforementioned conditions, it is heap-allocated
+* Additionally, a `SmolStr` can be explicitly created from a `&'static str` without allocation
Unlike `String`, however, `SmolStr` is immutable. The primary use case for
`SmolStr` is a good enough default storage for tokens of typical programming
diff --git a/lib/smol_str/src/lib.rs b/lib/smol_str/src/lib.rs
index 692803e447..a27b14c0ad 100644
--- a/lib/smol_str/src/lib.rs
+++ b/lib/smol_str/src/lib.rs
@@ -26,6 +26,7 @@ use core::{
/// * Longer than 23 bytes, but substrings of `WS` (see below). Such strings consist
/// solely of consecutive newlines, followed by consecutive spaces
/// * If a string does not satisfy the aforementioned conditions, it is heap-allocated
+/// * Additionally, a `SmolStr` can be explicitely created from a `&'static str` without allocation
///
/// Unlike `String`, however, `SmolStr` is immutable. The primary use case for
/// `SmolStr` is a good enough default storage for tokens of typical programming
@@ -78,6 +79,17 @@ impl SmolStr {
})
}
+ /// Constructs a `SmolStr` from a statically allocated string.
+ ///
+ /// This never allocates.
+ #[inline(always)]
+ pub const fn new_static(text: &'static str) -> SmolStr {
+ // NOTE: this never uses the inline storage; if a canonical
+ // representation is needed, we could check for `len() < INLINE_CAP`
+ // and call `new_inline`, but this would mean an extra branch.
+ SmolStr(Repr::Static(text))
+ }
+
pub fn new<T>(text: T) -> SmolStr
where
T: AsRef<str>,
@@ -395,6 +407,11 @@ const N_NEWLINES: usize = 32;
const N_SPACES: usize = 128;
const WS: &str =
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n ";
+const _: () = {
+ assert!(WS.len() == N_NEWLINES + N_SPACES);
+ assert!(WS.as_bytes()[N_NEWLINES - 1] == b'\n');
+ assert!(WS.as_bytes()[N_NEWLINES] == b' ');
+};
#[derive(Clone, Copy, Debug)]
#[repr(u8)]
@@ -428,18 +445,15 @@ enum InlineSize {
#[derive(Clone, Debug)]
enum Repr {
Heap(Arc<str>),
+ Static(&'static str),
Inline {
len: InlineSize,
buf: [u8; INLINE_CAP],
},
- Substring {
- newlines: usize,
- spaces: usize,
- },
}
impl Repr {
- /// This function tries to create a new Repr::Inline or Repr::Substring
+ /// This function tries to create a new Repr::Inline or Repr::Static
/// If it isn't possible, this function returns None
fn new_on_stack<T>(text: T) -> Option<Self>
where
@@ -467,7 +481,8 @@ impl Repr {
let possible_space_count = len - newlines;
if possible_space_count <= N_SPACES && bytes[newlines..].iter().all(|&b| b == b' ') {
let spaces = possible_space_count;
- return Some(Repr::Substring { newlines, spaces });
+ let substring = &WS[N_NEWLINES - newlines..N_NEWLINES + spaces];
+ return Some(Repr::Static(substring));
}
}
None
@@ -484,8 +499,8 @@ impl Repr {
fn len(&self) -> usize {
match self {
Repr::Heap(data) => data.len(),
+ Repr::Static(data) => data.len(),
Repr::Inline { len, .. } => *len as usize,
- Repr::Substring { newlines, spaces } => *newlines + *spaces,
}
}
@@ -493,9 +508,8 @@ impl Repr {
fn is_empty(&self) -> bool {
match self {
Repr::Heap(data) => data.is_empty(),
+ Repr::Static(data) => data.is_empty(),
Repr::Inline { len, .. } => *len as u8 == 0,
- // A substring isn't created for an empty string.
- Repr::Substring { .. } => false,
}
}
@@ -503,17 +517,12 @@ impl Repr {
fn as_str(&self) -> &str {
match self {
Repr::Heap(data) => &*data,
+ Repr::Static(data) => data,
Repr::Inline { len, buf } => {
let len = *len as usize;
let buf = &buf[..len];
unsafe { ::core::str::from_utf8_unchecked(buf) }
}
- Repr::Substring { newlines, spaces } => {
- let newlines = *newlines;
- let spaces = *spaces;
- assert!(newlines <= N_NEWLINES && spaces <= N_SPACES);
- &WS[N_NEWLINES - newlines..N_NEWLINES + spaces]
- }
}
}
}