| use std::str::Chars; |
| |
| /// Peekable iterator over a char sequence. |
| /// |
| /// Next characters can be peeked via `nth_char` method, |
| /// and position can be shifted forward via `bump` method. |
| pub(crate) struct Cursor<'a> { |
| initial_len: usize, |
| chars: Chars<'a>, |
| #[cfg(debug_assertions)] |
| prev: char, |
| } |
| |
| pub(crate) const EOF_CHAR: char = '\0'; |
| |
| impl<'a> Cursor<'a> { |
| pub(crate) fn new(input: &'a str) -> Cursor<'a> { |
| Cursor { |
| initial_len: input.len(), |
| chars: input.chars(), |
| #[cfg(debug_assertions)] |
| prev: EOF_CHAR, |
| } |
| } |
| |
| /// Returns the last eaten symbol (or `'\0'` in release builds). |
| /// (For debug assertions only.) |
| pub(crate) fn prev(&self) -> char { |
| #[cfg(debug_assertions)] |
| { |
| self.prev |
| } |
| |
| #[cfg(not(debug_assertions))] |
| { |
| '\0' |
| } |
| } |
| |
| /// Returns nth character relative to the current cursor position. |
| /// If requested position doesn't exist, `EOF_CHAR` is returned. |
| /// However, getting `EOF_CHAR` doesn't always mean actual end of file, |
| /// it should be checked with `is_eof` method. |
| fn nth_char(&self, n: usize) -> char { |
| self.chars().nth(n).unwrap_or(EOF_CHAR) |
| } |
| |
| /// Peeks the next symbol from the input stream without consuming it. |
| pub(crate) fn first(&self) -> char { |
| self.nth_char(0) |
| } |
| |
| /// Peeks the second symbol from the input stream without consuming it. |
| pub(crate) fn second(&self) -> char { |
| self.nth_char(1) |
| } |
| |
| /// Checks if there is nothing more to consume. |
| pub(crate) fn is_eof(&self) -> bool { |
| self.chars.as_str().is_empty() |
| } |
| |
| /// Returns amount of already consumed symbols. |
| pub(crate) fn len_consumed(&self) -> usize { |
| self.initial_len - self.chars.as_str().len() |
| } |
| |
| /// Returns a `Chars` iterator over the remaining characters. |
| fn chars(&self) -> Chars<'a> { |
| self.chars.clone() |
| } |
| |
| /// Moves to the next character. |
| pub(crate) fn bump(&mut self) -> Option<char> { |
| let c = self.chars.next()?; |
| |
| #[cfg(debug_assertions)] |
| { |
| self.prev = c; |
| } |
| |
| Some(c) |
| } |
| } |