94 lines
2.7 KiB
Rust
94 lines
2.7 KiB
Rust
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use crate::input::Input;
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use arraydeque::ArrayDeque;
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/// The size of the [`BufferedInput`] buffer.
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///
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/// The buffer is statically allocated to avoid conditions for reallocations each time we
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/// consume/push a character. As of now, almost all lookaheads are 4 characters maximum, except:
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/// - Escape sequences parsing: some escape codes are 8 characters
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/// - Scanning indent in scalars: this looks ahead `indent + 2` characters
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///
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/// This constant must be set to at least 8. When scanning indent in scalars, the lookahead is done
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/// in a single call if and only if the indent is `BUFFER_LEN - 2` or less. If the indent is higher
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/// than that, the code will fall back to a loop of lookaheads.
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const BUFFER_LEN: usize = 16;
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/// A wrapper around an [`Iterator`] of [`char`]s with a buffer.
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///
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/// The YAML scanner often needs some lookahead. With fully allocated buffers such as `String` or
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/// `&str`, this is not an issue. However, with streams, we need to have a way of peeking multiple
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/// characters at a time and sometimes pushing some back into the stream.
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/// There is no "easy" way of doing this without itertools. In order to avoid pulling the entierty
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/// of itertools for one method, we use this structure.
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pub struct BufferedInput<T: Iterator<Item = char>> {
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/// The iterator source,
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input: T,
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/// Buffer for the next characters to consume.
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buffer: ArrayDeque<char, BUFFER_LEN>,
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}
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impl<T: Iterator<Item = char>> BufferedInput<T> {
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/// Create a new [`BufferedInput`] with the given input.
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pub fn new(input: T) -> Self {
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Self {
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input,
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buffer: ArrayDeque::default(),
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}
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}
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}
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impl<T: Iterator<Item = char>> Input for BufferedInput<T> {
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#[inline]
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fn lookahead(&mut self, count: usize) {
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if self.buffer.len() >= count {
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return;
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}
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for _ in 0..(count - self.buffer.len()) {
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self.buffer
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.push_back(self.input.next().unwrap_or('\0'))
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.unwrap();
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}
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}
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#[inline]
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fn buflen(&self) -> usize {
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self.buffer.len()
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}
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#[inline]
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fn bufmaxlen(&self) -> usize {
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BUFFER_LEN
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}
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#[inline]
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fn raw_read_ch(&mut self) -> char {
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self.input.next().unwrap_or('\0')
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}
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#[inline]
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fn push_back(&mut self, c: char) {
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self.buffer.push_back(c).unwrap();
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}
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#[inline]
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fn skip(&mut self) {
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self.buffer.pop_front();
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}
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#[inline]
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fn skip_n(&mut self, count: usize) {
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self.buffer.drain(0..count);
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}
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#[inline]
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fn peek(&self) -> char {
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self.buffer[0]
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}
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#[inline]
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fn peek_nth(&self, n: usize) -> char {
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self.buffer[n]
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}
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}
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