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pub(crate) trait Splitter: Copy {
/// If any of the needles was found in the haystack, then split the haystack at the first hit.
///
/// Since only the first byte of a needle is inspected, be aware that there can be
/// false-positives. Always compare the latter string of the output if it fits the expected
/// prefix.
fn split<'a>(&self, haystack: &'a str) -> Option<(&'a str, &'a str)>;
}
impl<T: Splitter> Splitter for &T {
#[inline]
fn split<'a>(&self, haystack: &'a str) -> Option<(&'a str, &'a str)> {
T::split(self, haystack)
}
}
// define and implement a string splitter using memchr
macro_rules! new_memchr_type {
($struct:ident $split_unchecked:ident $memchr:ident $($field:ident)*) => {
#[derive(Debug, Clone, Copy)]
pub(crate) struct $struct {
$($field: u8,)*
}
impl $struct {
#[track_caller]
pub(crate) fn new($($field: &str),*) -> Self {
Self {
$($field: $field.as_bytes()[0],)*
}
}
#[inline]
pub(crate) fn split<'a>(&self, haystack: &'a str) -> Option<(&'a str, &'a str)> {
// SAFETY: During the construction of `self` we used strings as inputs, and a
// string always starts with a byte at char boundary.
unsafe { $split_unchecked($(self.$field,)* haystack) }
}
}
impl Splitter for $struct {
#[inline]
fn split<'a>(&self, haystack: &'a str) -> Option<(&'a str, &'a str)> {
self.split(haystack)
}
}
/// SAFETY: caller has to ensure that the needle is at a char boundary
pub(crate) unsafe fn $split_unchecked(
$($field: u8,)*
haystack: &str,
) -> Option<(&str, &str)> {
let idx = memchr::$memchr($($field,)* haystack.as_bytes())?;
// SAFETY: The caller ensures that the needles are at char boundary.
// The found index `< haystack.len()`.
Some((haystack.get_unchecked(..idx), haystack.get_unchecked(idx..)))
}
};
}
new_memchr_type!(Splitter1 split1_unchecked memchr a);
new_memchr_type!(Splitter2 split2_unchecked memchr2 a b);
new_memchr_type!(Splitter3 split3_unchecked memchr3 a b c);
#[test]
fn candidate_finder() {
assert_eq!(
Splitter1::new("test").split("abctefg"),
Some(("abc", "tefg")),
);
assert_eq!(Splitter1::new("xyz").split("abctefg"), None);
assert_eq!(
Splitter2::new("xyz", "foo").split("abctefg"),
Some(("abcte", "fg")),
);
assert_eq!(Splitter2::new("oof", "xyz").split("abctefg"), None);
assert_eq!(
Splitter3::new("oof", "apples", "xyz").split("abctefg"),
Some(("", "abctefg")),
);
assert_eq!(
Splitter3::new("oof", "peaches", "xyz").split("abctefg"),
None
);
assert_eq!(
Splitter3::new("test", "test", "test").split("abctefg"),
Some(("abc", "tefg")),
);
assert_eq!(
Splitter3::new("🧚♀️Life", "😀Laugh", "😻Love")
.split("sed diam nonumy eirmod tempor 🧚♀️Life ut labore et dolore magna aliquyam"),
Some((
"sed diam nonumy eirmod tempor ",
"🧚♀️Life ut labore et dolore magna aliquyam"
)),
);
}