Rust Pattern

简单的写法

1#[allow(dead_code)]
2fn output(filename: &str, bytes: &[u8]) -> Result<()> {
3    let mut fp = OpenOptions::new().truncate(true).create(true).write(true).open(Path::new(filename)).chain_err(|| format!("fail to open {}", filename))?;
4    fp.write_all( bytes )?;
5    fp.write_all( &['\n' as u8] )?;
6    fp.flush()?;
7
8    Ok(())
9}

或者，如下写法更有 Rust 的感觉

1#[allow(dead_code)]
2fn output(filename: &str, bytes: &[u8]) -> Result<()> {
3    OpenOptions::new().truncate(true).create(true).write(true).open(Path::new(filename)).and_then(|mut fp| {
4        fp.write_all( bytes )?;
5        fp.write_all( &['\n' as u8] )?;
6        fp.flush()?;
7        
8        Ok(())
9    })
10}

引入 BufWriter， 增加写缓冲

1#[allow(dead_code)]
2fn output(filename: &str, bytes: &[u8]) -> Result<()> {
3    let fp = OpenOptions::new().truncate(true).create(true).write(true).open(Path::new(filename)).chain_err(|| format!("fail to open {}", filename))?;
4    let mut writer = BufWriter::with_capacity( 1024*1024*4, fp );
5    writer.write_all( bytes )?;
6    writer.write_all( &['\n' as u8] )?;
7    writer.flush()?;
8
9    Ok(())
10}

当 filename == '-' 时，写到标准输出（STDOUT）

1#[allow(dead_code)]
2fn output(filename: &str, bytes: &[u8]) -> Result<()> {
3    let fp = match filename {
4        "-" => Box::new(stdout()) as Box<Write>,
5        filename => {
6            let path = Path::new(filename);
7            //let fp = OpenOptions::new().append(true).create(true).write(true).open(path).unwrap();
8            let fp = OpenOptions::new().truncate(true).create(true).write(true).open(path).unwrap();
9            Box::new(fp) as Box<Write>
10        },
11    };
12
13    let mut writer = BufWriter::with_capacity( 1024*1024*4, fp );
14    writer.write_all( bytes )?;
15    writer.write_all( &['\n' as u8] )?;
16    writer.flush()?;
17
18    Ok(())
19}