项目实战

实战2：命令行工具minigrep

我们继续开发我们的minigrep。

我们现在以TDD测试驱动开发的模式，来开发新的功能search函数。

开始吧，我们先在ｓｒｃ／ｌｉｂ．ｒｓ文件中，增加测试代码：

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn one_result() {

        let query = "duct";

        let contents = "\

Rust:

safe, fast, productive.

Pick three.";

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

    }

}

然后同样再写一个空函数：

pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {

    vec![]

}

然后，我们要跑一下命令：

cargo test

结果显示：

$ cargo test

   Compiling minigrep v0.1.0 (file:///projects/minigrep)

--warnings--

    Finished dev [unoptimized + debuginfo] target(s) in 0.43 secs

     Running target/debug/deps/minigrep-abcabcabc

running 1 test

test tests::one_result ... FAILED

failures:

---- tests::one_result stdout ----

        thread 'tests::one_result' panicked at 'assertion failed: `(left ==

right)`

left: `["safe, fast, productive."]`,

right: `[]`)', src/lib.rs:48:8

note: Run with `RUST_BACKTRACE=1` for a backtrace.

failures:

    tests::one_result

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

error: test failed, to rerun pass '--lib'

测试不通过。

我们的实现函数search，只简单返回一个空vector。当然，不通过。

怎么办？

重构一下search函数：

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

}

然后，我们跑一下命令：

cargo test

结果显示：

running 1 test

test tests::one_result ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

测试通过！漂亮！

这就是TDD的基本流程。

我们看看示图：

好吧，现在我们可以直接调用search函数了，把它放到src/lib.rs中的run函数里：

//重构从文件中读取内容的业务逻辑

pub fn run(config: Config) -> Result<(), Box<dyn Error>> {

    let contents = fs::read_to_string(config.filename)?;

    println!("With text:\n{}", contents);

    for line in search(&config.query, &contents) {

       println!("-----search result ------{}", line);

    }

    Ok(())

}

然后，我们用运行命令：

cargo run frog poem.txt

结果为：

.......

-----search result ------How public, like a frog

我们找到包含frog单词的那一行！完美！

我们再找下body单词：

cargo run body poem.txt

结果为：

......

-----search result ------I'm nobody! Who are you?

-----search result ------Are you nobody, too?

-----search result ------How dreary to be somebody!

结果正确！

当然，我们也可以试试不存在的单词：

cargo run monomorphization poem.txt

结果为：

E:\code\rustProject\minigrep> cargo run monomorphization poem.txt

    Finished dev [unoptimized + debuginfo] target(s) in 0.01s

     Running `target\debug\minigrep.exe monomorphization poem.txt`

With text:

I'm nobody! Who are you?

Are you nobody, too?

Then there's a pair of us - don't tell!

They'd banish us, you know.

How dreary to be somebody!

How public, like a frog

To tell your name the livelong day

To an admiring bog!

没有出现带“-----search result ------”的结果信息，说明没有找到单词：monomorphization。

结果符合期望。

现在我们再以TDD的开发方式来开发新的功能函数search_case_insensitive，新增测试代码：

#[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)

    );

}

当然，我们可以简单实现一下search_case_insensitive函数，让它fail，因为这个逻辑比较简单，那就直接实现吧：

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

}

好的，我们跑一下命令：

cargo test

结果：

$cargo test

   Compiling minigrep v0.1.0 (E:\code\rustProject\minigrep)

    Finished dev [unoptimized + debuginfo] target(s) in 1.38s

     Running target\debug\deps\minigrep-07da7ef1bffd9ef9.exe

running 2 tests

test case_insensitive ... ok

test tests::one_result ... ok

测试通过，漂亮！

我们现在把这个方法整合到run函数里：

//重构从文件中读取内容的业务逻辑

pub fn run(config: Config) -> Result<(), Box<dyn Error>> {

    let contents = fs::read_to_string(config.filename)?;

    println!("With text:\n{}", contents);

    let results = if config.case_sensitive {

        search(&config.query, &contents)

    } else {

        search_case_insensitive(&config.query, &contents)

    };

    for line in results {

        println!("-----search result ------{}", line);

    }

    Ok(())

}

当然，我们也要把属性case_sensitive放到结构体Config里面：

//结构体Config用来封装参数属性

pub struct Config {

    pub query: String,

    pub filename: String,

    pub case_sensitive: bool,

}

src/lib.rs的完整代码如下：

use std::env;

use std::error::Error;

use std::fs;

//结构体Config用来封装参数属性

pub struct Config {

    pub query: String,

    pub filename: String,

    pub case_sensitive: bool,

}

//为结构体实现一个构造器，其主要功能也是读取和解析参数

impl Config {

    pub fn new(args: &[String]) -> Result<Config, &'static str> {

        if args.len() < 3 {

            return Err("参数个数不够！not enough arguments");

        }

        let query = args[1].clone();

        let filename = args[2].clone();

        let case_sensitive = env::var("CASE_INSENSITIVE").is_err();

        Ok(Config {

            query,

            filename,

            case_sensitive,

        })

    }

}

//重构从文件中读取内容的业务逻辑

pub fn run(config: Config) -> Result<(), Box<dyn Error>> {

    let contents = fs::read_to_string(config.filename)?;

    println!("With text:\n{}", contents);

    let results = if config.case_sensitive {

        search(&config.query, &contents)

    } else {

        search_case_insensitive(&config.query, &contents)

    };

    for line in results {

        println!("-----search result ------{}", line);

    }

    Ok(())

}

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

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn one_result() {

        let query = "duct";

        let contents = "\

Rust:

safe, fast, productive.

Pick three.";

        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)

    );

}

我们现在运行命令：

cargo run to poem.txt

结果:

......

-----search result ------Are you nobody, too?

-----search result ------How dreary to be somebody!

现在我们把环境变量设置一下：

如果你的终端是powershell，用以下命令

 $env:CASE_INSENSITIVE=1

我们现在运行命令：

cargo run to poem.txt

结果:

......

-----search result ------Are you nobody, too?

-----search result ------How dreary to be somebody!

-----search result ------To tell your name the livelong day

-----search result ------To an admiring bog!

我们现在看看把错误信息输出到一个output.txt文件，运行以下命令：

cargo run > output.txt

我们观察到，控制台没有输出。

但当前工程目录有一个output.txt文件，打开文件。里面有错误信息。

我们现在来用eprintln!宏替换掉println!宏。src/main.rs代码更新如下：

use minigrep::run;

use minigrep::Config;

use std::env;

use std::process;

//主函数，程序入口

fn main() {

    let args: Vec<String> = env::args().collect();

    let config = Config::new(&args).unwrap_or_else(|err| {

        eprintln!("Problem parsing arguments: {}", err);

        process::exit(1);

    });

    if let Err(e) = run(config) {

        //根据处理结果返回值 来处理，如果有错误，则打印信息，并直接退出当前程序

        eprintln!("Application error: {}", e);

        process::exit(1);

    }

}

运行以下命令：

cargo run > output.txt

我们观察到，控制台现在会输出错误信息。

我们运行如下命令：

 cargo run to poem.txt > output.txt

这里控制台没有输出。

但打开output.txt，里面的信息为：

With text:

I'm nobody! Who are you?

Are you nobody, too?

Then there's a pair of us - don't tell!

They'd banish us, you know.

How dreary to be somebody!

How public, like a frog

To tell your name the livelong day

To an admiring bog!

-----search result ------Are you nobody, too?

-----search result ------How dreary to be somebody!

-----search result ------To tell your name the livelong day

-----search result ------To an admiring bog!

以上，希望对你有用。

如果遇到什么问题，欢迎加入：rust新手群，在这里我可以提供一些简单的帮助，加微信：360369487，注明：博客园+rust

参考文章：

https://doc.rust-lang.org/stable/book/ch12-05-working-with-environment-variables.html

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实战2：命令行工具minigrep

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