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Commit | Line | Data |
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416331ca XL |
1 | use std::str::Chars; |
2 | ||
e74abb32 XL |
3 | /// Peekable iterator over a char sequence. |
4 | /// | |
a2a8927a | 5 | /// Next characters can be peeked via `first` method, |
e74abb32 | 6 | /// and position can be shifted forward via `bump` method. |
2b03887a FG |
7 | pub struct Cursor<'a> { |
8 | len_remaining: usize, | |
a2a8927a | 9 | /// Iterator over chars. Slightly faster than a &str. |
416331ca XL |
10 | chars: Chars<'a>, |
11 | #[cfg(debug_assertions)] | |
12 | prev: char, | |
13 | } | |
14 | ||
15 | pub(crate) const EOF_CHAR: char = '\0'; | |
16 | ||
17 | impl<'a> Cursor<'a> { | |
2b03887a | 18 | pub fn new(input: &'a str) -> Cursor<'a> { |
416331ca | 19 | Cursor { |
2b03887a | 20 | len_remaining: input.len(), |
416331ca XL |
21 | chars: input.chars(), |
22 | #[cfg(debug_assertions)] | |
23 | prev: EOF_CHAR, | |
24 | } | |
25 | } | |
e74abb32 | 26 | |
f035d41b XL |
27 | /// Returns the last eaten symbol (or `'\0'` in release builds). |
28 | /// (For debug assertions only.) | |
416331ca XL |
29 | pub(crate) fn prev(&self) -> char { |
30 | #[cfg(debug_assertions)] | |
31 | { | |
32 | self.prev | |
33 | } | |
34 | ||
35 | #[cfg(not(debug_assertions))] | |
36 | { | |
5869c6ff | 37 | EOF_CHAR |
416331ca XL |
38 | } |
39 | } | |
e74abb32 | 40 | |
a2a8927a | 41 | /// Peeks the next symbol from the input stream without consuming it. |
e74abb32 XL |
42 | /// If requested position doesn't exist, `EOF_CHAR` is returned. |
43 | /// However, getting `EOF_CHAR` doesn't always mean actual end of file, | |
44 | /// it should be checked with `is_eof` method. | |
60c5eb7d | 45 | pub(crate) fn first(&self) -> char { |
a2a8927a XL |
46 | // `.next()` optimizes better than `.nth(0)` |
47 | self.chars.clone().next().unwrap_or(EOF_CHAR) | |
60c5eb7d XL |
48 | } |
49 | ||
50 | /// Peeks the second symbol from the input stream without consuming it. | |
51 | pub(crate) fn second(&self) -> char { | |
a2a8927a XL |
52 | // `.next()` optimizes better than `.nth(1)` |
53 | let mut iter = self.chars.clone(); | |
54 | iter.next(); | |
55 | iter.next().unwrap_or(EOF_CHAR) | |
60c5eb7d XL |
56 | } |
57 | ||
e74abb32 | 58 | /// Checks if there is nothing more to consume. |
416331ca XL |
59 | pub(crate) fn is_eof(&self) -> bool { |
60 | self.chars.as_str().is_empty() | |
61 | } | |
e74abb32 XL |
62 | |
63 | /// Returns amount of already consumed symbols. | |
2b03887a FG |
64 | pub(crate) fn pos_within_token(&self) -> u32 { |
65 | (self.len_remaining - self.chars.as_str().len()) as u32 | |
416331ca | 66 | } |
e74abb32 | 67 | |
a2a8927a | 68 | /// Resets the number of bytes consumed to 0. |
2b03887a FG |
69 | pub(crate) fn reset_pos_within_token(&mut self) { |
70 | self.len_remaining = self.chars.as_str().len(); | |
416331ca | 71 | } |
e74abb32 | 72 | |
416331ca XL |
73 | /// Moves to the next character. |
74 | pub(crate) fn bump(&mut self) -> Option<char> { | |
75 | let c = self.chars.next()?; | |
76 | ||
77 | #[cfg(debug_assertions)] | |
78 | { | |
79 | self.prev = c; | |
80 | } | |
81 | ||
82 | Some(c) | |
83 | } | |
a2a8927a XL |
84 | |
85 | /// Eats symbols while predicate returns true or until the end of file is reached. | |
86 | pub(crate) fn eat_while(&mut self, mut predicate: impl FnMut(char) -> bool) { | |
87 | // It was tried making optimized version of this for eg. line comments, but | |
88 | // LLVM can inline all of this and compile it down to fast iteration over bytes. | |
89 | while predicate(self.first()) && !self.is_eof() { | |
90 | self.bump(); | |
91 | } | |
92 | } | |
416331ca | 93 | } |