今年の言語はRust その３２


# 今年の言語はRust その３２

Rustを学びます

Rustの日本語ドキュメント 2nd Edition
https://doc.rust-jp.rs/book/second-edition/

オリジナル(英語)
https://doc.rust-lang.org/book/


## 実行環境

```sh
$ cargo -V
cargo 1.33.0 (f099fe94b 2019-02-12)

$ rustup -V
rustup 1.17.0 (069c88ed6 2019-03-05)

$ rustc --version
rustc 1.33.0 (2aa4c46cf 2019-02-28)

$  cat /proc/version
Linux version 4.14.97-74.72.amzn1.x86_64 (mockbuild@gobi-build-64002) 
(gcc version 7.2.1 20170915 (Red Hat 7.2.1-2) (GCC)) 
#1 SMP Tue Feb 5 20:59:30 UTC 2019

$ uname -a
Linux ip-10-100-0-8 4.14.97-74.72.amzn1.x86_64 
#1 SMP Tue Feb 5 20:59:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

$ cat /etc/\*release
NAME="Amazon Linux AMI"
VERSION="2018.03"
ID="amzn"
ID_LIKE="rhel fedora"
VERSION_ID="2018.03"
PRETTY_NAME="Amazon Linux AMI 2018.03"
ANSI_COLOR="0;33"
CPE_NAME="cpe:/o:amazon:linux:2018.03:ga"
HOME_URL="http://aws.amazon.com/amazon-linux-ami/"
Amazon Linux AMI release 2018.03

```


## 12 入出力プロジェクト
コマンドラインプログラムを構築する

### 12.5 環境変数を取り扱う

```rust


#[cfg(test)]
mod test {

    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_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)
            );
    }
}
```

大文字も小文字も気にせず検索できる関数を立てる

```rust
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
}
```

オプションを追加します。


```rust
pub struct Config {
    pub query: String,
    pub filename: String,
    pub case_sensitive: bool,
}
```

```rust

pub fn run(config: Config) -> Result<(), Box<Error>> {
    let mut f = File::open(config.filename)?;

    let mut contents = String::new();
    f.read_to_string(&mut contents)?;

    let results = if config.case_sensitive {
        search(&config.query, &contents)
    } else {
        search_case_insensitive(&config.query, &contents)
    };

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

    Ok(())
}
```



さてポイントとなる環境変数の受け取り方法です。

__env::var__ 使います。

__注意__ 環境変数の__値__ ではなくて、 __存在の有無__ を読み取っているだけです。

```rust
impl Config {
    pub fn new(args: &[String]) -> Result<Config, &'static str> {
    
        if args.len() < 3 {
            return Err("not enough arguments");
        }

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


```rust
$ CASE_INSENSITIVE=hoge cargo run TO poem.txt

Are you nobody, too?
How dreary to be somebody!
To tell your name the livelong day
To an admiring bog!
nohara:~/environment/minigrep (master) 
```

```rust
$ CASE_INSENSITIVE=1 cargo run TO poem.txt             

Are you nobody, too?
How dreary to be somebody!
To tell your name the livelong day
To an admiring bog!
nohara:~/environment/minigrep (master) 
```

```rust
$ cargo run TO poem.txt


// 検索結果なし

```

> std::envモジュールは、環境変数を扱うもっと多くの有用な機能を有しています: ドキュメンテーションを確認して、何が利用可能か確かめてください。





イエス！