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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 | /// | |
5 | /// Next characters can be peeked via `nth_char` method, | |
6 | /// and position can be shifted forward via `bump` method. | |
416331ca XL |
7 | pub(crate) struct Cursor<'a> { |
8 | initial_len: usize, | |
9 | chars: Chars<'a>, | |
10 | #[cfg(debug_assertions)] | |
11 | prev: char, | |
12 | } | |
13 | ||
14 | pub(crate) const EOF_CHAR: char = '\0'; | |
15 | ||
16 | impl<'a> Cursor<'a> { | |
17 | pub(crate) fn new(input: &'a str) -> Cursor<'a> { | |
18 | Cursor { | |
19 | initial_len: input.len(), | |
20 | chars: input.chars(), | |
21 | #[cfg(debug_assertions)] | |
22 | prev: EOF_CHAR, | |
23 | } | |
24 | } | |
e74abb32 | 25 | |
f035d41b XL |
26 | /// Returns the last eaten symbol (or `'\0'` in release builds). |
27 | /// (For debug assertions only.) | |
416331ca XL |
28 | pub(crate) fn prev(&self) -> char { |
29 | #[cfg(debug_assertions)] | |
30 | { | |
31 | self.prev | |
32 | } | |
33 | ||
34 | #[cfg(not(debug_assertions))] | |
35 | { | |
36 | '\0' | |
37 | } | |
38 | } | |
e74abb32 XL |
39 | |
40 | /// Returns nth character relative to the current cursor position. | |
41 | /// If requested position doesn't exist, `EOF_CHAR` is returned. | |
42 | /// However, getting `EOF_CHAR` doesn't always mean actual end of file, | |
43 | /// it should be checked with `is_eof` method. | |
60c5eb7d | 44 | fn nth_char(&self, n: usize) -> char { |
416331ca XL |
45 | self.chars().nth(n).unwrap_or(EOF_CHAR) |
46 | } | |
e74abb32 | 47 | |
60c5eb7d XL |
48 | /// Peeks the next symbol from the input stream without consuming it. |
49 | pub(crate) fn first(&self) -> char { | |
50 | self.nth_char(0) | |
51 | } | |
52 | ||
53 | /// Peeks the second symbol from the input stream without consuming it. | |
54 | pub(crate) fn second(&self) -> char { | |
55 | self.nth_char(1) | |
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. | |
416331ca XL |
64 | pub(crate) fn len_consumed(&self) -> usize { |
65 | self.initial_len - self.chars.as_str().len() | |
66 | } | |
e74abb32 XL |
67 | |
68 | /// Returns a `Chars` iterator over the remaining characters. | |
416331ca XL |
69 | fn chars(&self) -> Chars<'a> { |
70 | self.chars.clone() | |
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 | } | |
84 | } |