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//! 読み取りと組み上げに失敗したときのエラー
use std::fmt;
/// 失敗した理由と、元の文字列でのその位置
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Error {
/// 何が起きたかの説明
pub message: String,
/// 元の文字列の先頭から数えた文字位置 (0 始まり)
pub position: usize,
}
impl Error {
pub fn new(message: impl Into<String>, position: usize) -> Error {
Error {message: message.into(), position}
}
}
impl fmt::Display for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
write!(formatter, "{} ({} 文字目)", self.message, self.position + 1)
}
}
impl std::error::Error for Error {}
/// 文字位置を行と桁に直す。どちらも 1 から数える
pub fn place(source: &[char], position: usize) -> (usize, usize) {
let mut line = 1;
let mut column = 1;
for character in source.iter().take(position) {
if *character == '\n' {
line += 1;
column = 1;
} else {
column += 1;
}
}
(line, column)
}
/// 誤りの位置を行と桁で言い直す
pub fn describe(source: &[char], error: &Error) -> String {
let (line, column) = place(source, error.position);
format!("{line} 行 {column} 桁: {}", error.message)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn a_position_becomes_a_line_and_a_column() {
let source: Vec<char> = "abc\ndef".chars().collect();
assert_eq!(place(&source, 0), (1, 1));
assert_eq!(place(&source, 4), (2, 1));
assert_eq!(place(&source, 6), (2, 3));
}
}
