为什么String与String无法使用 == 比较？

use std::io; use std::fmt::{Debug, Display, Formatter, Result}; macro_rules! parse_input { ($x:expr, $t:ident) => ($x.trim().parse::<$t>().unwrap()) } #[derive(Debug, Clone, Copy)] enum LogLevel { FATAL, ERROR, WARNING, INFO, DEBUG, UNKNOW } impl Display for LogLevel { fn fmt(&self, f: &mut Formatter) -> Result { match self { LogLevel::FATAL => write!(f, "FATAL"), LogLevel::ERROR => write!(f, "ERROR"), LogLevel::WARNING => write!(f, "WARING"), LogLevel::INFO => write!(f, "WARING"), LogLevel::DEBUG => write!(f, "DEBUG"), _ => write!(f, "UNKNOW") } } } impl From<LogLevel> for String { fn from(level: LogLevel) -> Self{ println!("FATAL impl form"); match level { LogLevel::FATAL => "FATAL".into(), LogLevel::ERROR => "ERROR".into(), LogLevel::WARNING => "WARNING".into(), LogLevel::INFO => "INFO".into(), LogLevel::DEBUG => "DEBUG".into(), LogLevel::UNKNOW => "UNKNOW".into() } } } impl From<String> for LogLevel { fn from(level: String) -> Self { match level { // 为什么这里不能比较？ level if level == LogLevel::FATAL.to_string() => { println!("FATAL for LogLevel : {}", level); LogLevel::FATAL }, level if level == LogLevel::ERROR.to_string() || level == "ERR" => LogLevel::ERROR, level if level == LogLevel::WARNING.to_string() || level =="WARN" => LogLevel::WARNING, level if level == LogLevel::INFO.to_string() => LogLevel::INFO, level if level == LogLevel::DEBUG.to_string() => { println!("DEBUG for LogLevel : {}", level); LogLevel::DEBUG }, _ => { // 为什么用 level 的值是FATAL会到这里来？ println!("Default for LogLevel : {}", level); LogLevel::UNKNOW } } } } /** * Auto-generated code below aims at helping you parse * the standard input according to the problem statement. **/ fn main() { let mut input_line = String::new(); io::stdin().read_line(&mut input_line).unwrap(); let lvl = parse_input!(input_line, i32); // println!("lvl: {}", lvl); let mut input_line = String::new(); io::stdin().read_line(&mut input_line).unwrap(); let n = parse_input!(input_line, i32); for _i in (0..n as usize) { let mut input_line = String::new(); io::stdin().read_line(&mut input_line).unwrap(); let line = input_line.trim_matches('\n').to_string(); // println!("line: {}", line); let mut split = line.split('>'); split.next(); let condition = split.next().unwrap(); // FATAL: could not // println!("condition: {}", condition); let mut split = condition.split(':'); let level_str = split.next().unwrap(); println!("level charactor: {}", level_str); let level: LogLevel = level_str.to_string().into(); println!("level: {}", level); let level_number = level as i32; println!("LEVEL:{}, level: {}, lvl: {}, level <= lvl: {}", level, level_number, lvl, level_number <= lvl); if level_number <= lvl { println!("{}", line); } } // Write an answer using println!("message..."); // To debug: eprintln!("Debug message..."); } Input: 2 2 <Easyone> FATAL: could not start Easyone software. Verify connectivity <Easyone> DEBUG: 239 1239 122 1 Standard Output Stream: level charactor: FATAL Default for LogLevel : FATAL level: UNKNOW LEVEL:UNKNOW, level: 5, lvl: 2, level <= lvl: false level charactor: DEBUG Default for LogLevel : DEBUG level: UNKNOW LEVEL:UNKNOW, level: 5, lvl: 2, level <= lvl: false