Rust Lang Book Ch.12 An I/O Project: Building a Command Line Program

src/lib.rs

use std::error::Error;
use std::fs;

struct Config {
    pub query: String,
    pub filename: String,
    pub case_sensitive: bool,
}
impl Config {
    fn new(args: &[String]) -> Result<Config, &'static str> {
        if args.len() < 3 {
            return Err("not enough arguments");//返回string literal，所以可以用'static，也就是说生成了之后就一直有效
        }

        let query = args[1].clone();
        let filename = args[2].clone();
// CASE_INSENSITIVE=1时为true
        let case_sensitive = env::var("CASE_INSENSITIVE").is_err();
		
        Ok(Config { query, filename })
    }
}

pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let mut results = Vec::new();

    for line in contents.lines() {
        if line.contains(query) {
            results.push(line);
        }
    }

    results
}

pub fn search_case_insensitive<'a>(
    query: &str,
    contents: &'a str,
) -> Vec<&'a str> {
    let query = query.to_lowercase();
    let mut results = Vec::new();

    for line in contents.lines() {
        if line.to_lowercase().contains(&query) {
            results.push(line);
        }
    }

    results
}

fn run(config: Config) -> Result<(), Box<dyn Error>> {
//Box<dyn Error> 返回一个能够实现Error特性的类型 dyn: dynamic
    let contents = fs::read_to_string(config.filename)?;//错误传递
    let results = if config.case_sensitive {
        search(&config.query, &contents)
    } else {
        search_case_insensitive(&config.query, &contents)
    };//if{}else{}是一个expression

    for line in results {
        println!("{}", line);
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn case_sensitive() {
        let query = "duct";
        let contents = "\
Rust:
safe, fast, productive.
Pick three.
Duct tape.";

        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
    }

    #[test]
    fn case_insensitive() {
        let query = "rUsT";
        let contents = "\
Rust:
safe, fast, productive.
Pick three.
Trust me.";

        assert_eq!(
            vec!["Rust:", "Trust me."],
            search_case_insensitive(query, contents)
        );
    }
}

　　

src/main.rs

use std::env;
use std::process;

use minigrep::Config;
fn main() {
    let args: Vec<String> = env::args().collect();
//std::env::args如果接收到invalid Unicode就会panic。如果包含这样的字符，可以使用std::env::args_os来代替，用OsString来兼容这些字符

    let config = Config::new(&args).unwrap_or_else(|err| {
//如果static string "not enough arguments"作为err这个变量被返回了，那就执行接下来的逻辑
        eprintln!("Problem parsing arguments: {}", err);
        process::exit(1);
    });

    println!("Searching for {}", config.query);
    println!("In file {}", config.filename);
	
    if let Err(e) = run(config) {
        eprintln!("Application error: {}", e);

        process::exit(1);
    }
}