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use std::slice::SliceIndex;
/// A featureful char-based scanner.
#[derive(Copy, Clone)]
pub struct Scanner<'s> {
/// The string to scan.
src: &'s str,
/// The index at which the peekable character starts. Must be in bounds and
/// at a codepoint boundary to guarantee safety.
index: usize,
}
impl<'s> Scanner<'s> {
/// Create a new char scanner.
#[inline]
pub fn new(src: &'s str) -> Self {
Self { src, index: 0 }
}
/// Consume the next char.
#[inline]
pub fn eat(&mut self) -> Option<char> {
let next = self.peek();
if let Some(c) = next {
self.index += c.len_utf8();
}
next
}
/// Consume the next char if it is the given one.
///
/// Returns whether the char was consumed.
#[inline]
pub fn eat_if(&mut self, c: char) -> bool {
let matches = self.peek() == Some(c);
if matches {
self.index += c.len_utf8();
}
matches
}
/// Consume the next char, debug-asserting that it is the given one.
#[inline]
pub fn eat_assert(&mut self, c: char) {
let next = self.eat();
debug_assert_eq!(next, Some(c));
}
/// Eat chars while the condition is true.
#[inline]
pub fn eat_while<F>(&mut self, mut f: F) -> &'s str
where
F: FnMut(char) -> bool,
{
self.eat_until(|c| !f(c))
}
/// Eat chars until the condition is true.
#[inline]
pub fn eat_until<F>(&mut self, mut f: F) -> &'s str
where
F: FnMut(char) -> bool,
{
let start = self.index;
while let Some(c) = self.peek() {
if f(c) {
break;
}
self.index += c.len_utf8();
}
self.eaten_from(start)
}
/// Uneat the last eaten char.
#[inline]
pub fn uneat(&mut self) {
self.index = self.last_index();
}
/// Peek at the next char without consuming it.
#[inline]
pub fn peek(&self) -> Option<char> {
self.rest().chars().next()
}
/// Checks whether the next char fulfills a condition.
///
/// Returns `default` if there is no next char.
#[inline]
pub fn check_or<F>(&self, default: bool, f: F) -> bool
where
F: FnOnce(char) -> bool,
{
self.peek().map_or(default, f)
}
/// The previous index in the source string.
#[inline]
pub fn last_index(&self) -> usize {
self.eaten().chars().last().map_or(0, |c| self.index - c.len_utf8())
}
/// The current index in the source string.
#[inline]
pub fn index(&self) -> usize {
self.index
}
/// Jump to an index in the source string.
#[inline]
pub fn jump(&mut self, index: usize) {
// Make sure that the index is in bounds and on a codepoint boundary.
self.src.get(index ..).expect("jumped to invalid index");
self.index = index;
}
/// Slice out part of the source string.
#[inline]
pub fn get<I>(&self, index: I) -> &'s str
where
I: SliceIndex<str, Output = str>,
{
// See `eaten_from` for details about `unwrap_or_default`.
self.src.get(index).unwrap_or_default()
}
/// The remaining source string after the current index.
#[inline]
pub fn rest(&self) -> &'s str {
// Safety: The index is always in bounds and on a codepoint boundary
// since it starts at zero and is is:
// - either increased by the length of a scanned character, advacing
// from one codepoint boundary to the next,
// - or checked upon jumping.
unsafe { self.src.get_unchecked(self.index ..) }
}
/// The full source string up to the current index.
#[inline]
pub fn eaten(&self) -> &'s str {
// Safety: The index is always okay, for details see `rest()`.
unsafe { self.src.get_unchecked(.. self.index) }
}
/// The source string from `start` to the current index.
#[inline]
pub fn eaten_from(&self, start: usize) -> &'s str {
// Using `unwrap_or_default` is much faster than unwrap, probably
// because then the whole call to `eaten_from` is pure and can be
// optimized away in some cases.
self.src.get(start .. self.index).unwrap_or_default()
}
}
/// Whether this character denotes a newline.
#[inline]
pub fn is_newline(character: char) -> bool {
matches!(
character,
// Line Feed, Vertical Tab, Form Feed, Carriage Return.
'\n' | '\x0B' | '\x0C' | '\r' |
// Next Line, Line Separator, Paragraph Separator.
'\u{0085}' | '\u{2028}' | '\u{2029}'
)
}
|
