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79 lines
2.0 KiB
79 lines
2.0 KiB
3 years ago
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use std::str::Chars;
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/// Peekable iterator over a char sequence.
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///
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/// Next characters can be peeked via `nth_char` method,
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/// and position can be shifted forward via `bump` method.
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pub(crate) struct Cursor<'a> {
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initial_len: usize,
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chars: Chars<'a>,
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prev: char,
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}
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pub(crate) const EOF_CHAR: char = '\0';
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impl<'a> Cursor<'a> {
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pub(crate) fn new(input: &'a str) -> Cursor<'a> {
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Cursor {
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initial_len: input.len(),
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chars: input.chars(),
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#[cfg(debug_assertions)]
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prev: EOF_CHAR,
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}
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}
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/// For debug assertions only
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/// Returns the last eaten symbol (or '\0' in release builds).
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pub(crate) fn prev(&self) -> char {
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#[cfg(debug_assertions)]
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{
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self.prev
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}
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#[cfg(not(debug_assertions))]
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{
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'\0'
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}
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}
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/// Returns nth character relative to the current cursor position.
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/// If requested position doesn't exist, `EOF_CHAR` is returned.
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/// However, getting `EOF_CHAR` doesn't always mean actual end of file,
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/// it should be checked with `is_eof` method.
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fn nth_char(&self, n: usize) -> char {
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self.chars().nth(n).unwrap_or(EOF_CHAR)
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}
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/// Peeks the next symbol from the input stream without consuming it.
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pub(crate) fn first(&self) -> char {
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self.nth_char(0)
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}
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/// Checks if there is nothing more to consume.
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pub(crate) fn is_eof(&self) -> bool {
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self.chars.as_str().is_empty()
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}
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/// Returns amount of already consumed symbols.
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pub(crate) fn len_consumed(&self) -> usize {
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self.initial_len - self.chars.as_str().len()
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}
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/// Returns a `Chars` iterator over the remaining characters.
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pub(crate) fn chars(&self) -> Chars<'a> {
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self.chars.clone()
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}
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/// Moves to the next character.
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pub(crate) fn bump(&mut self) -> Option<char> {
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let c = self.chars.next()?;
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#[cfg(debug_assertions)]
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{
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self.prev = c;
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}
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Some(c)
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}
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}
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