如何从 Rust 中的 File 或 stdin 进行多态 IO

我试图实现一个"多态"Input枚举，它隐藏了我们是从文件还是从stdin读取.更具体地说，我正在try 构建一个枚举，该枚举将有一个lines方法，该方法将把调用"委托"到BufReader中的File或StdInLock(两者都有lines()方法).

以下是枚举:

enum Input<'a> {
    Console(std::io::StdinLock<'a>),
    File(std::io::BufReader<std::fs::File>)
}

我有三种方法:

• from_arg用于通过判断是否提供了参数(文件名)来确定我们是从文件还是从标准输入文件中读取，
• 用BufReader包装一个文件，
• console用于锁定标准DIN.

实施:

impl<'a> Input<'a> {
    fn console() -> Input<'a> {
        Input::Console(io::stdin().lock())
    }

    fn file(path: String) -> io::Result<Input<'a>> {
        match File::open(path) {
            Ok(file) => Ok(Input::File(std::io::BufReader::new(file))),
            Err(_) => panic!("kita"),
        }
    }

    fn from_arg(arg: Option<String>) -> io::Result<Input<'a>> {
        Ok(match arg {
            None => Input::console(),
            Some(path) => try!(Input::file(path)),
        })
    }
}

据我所知，我必须实现BufRead个和Read个特征，这样才能工作.这是我的try :

impl<'a> io::Read for Input<'a> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        match *self {
            Input::Console(ref mut c) => c.read(buf),
            Input::File(ref mut f) => f.read(buf),
        }
    }
}

impl<'a> io::BufRead for Input<'a> {
    fn lines(self) -> Lines<Self> {
        match self {
            Input::Console(ref c) => c.lines(),
            Input::File(ref f) => f.lines(),
        }
    }

    fn consume(&mut self, amt: usize) {
        match *self {
            Input::Console(ref mut c) => c.consume(amt),
            Input::File(ref mut f) => f.consume(amt),
        }
    }

    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        match *self {
            Input::Console(ref mut c) => c.fill_buf(),
            Input::File(ref mut f) => f.fill_buf(),
        }
    }
}

最后，调用:

fn load_input<'a>() -> io::Result<Input<'a>> {
    Ok(try!(Input::from_arg(env::args().skip(1).next())))
}

fn main() {
    let mut input = match load_input() {
        Ok(input) => input,
        Err(error) => panic!("Failed: {}", error),
    };

    for line in input.lines() { /* do stuff */ }
}

Complete example in the playground

编译器告诉我模式匹配错误，我有mismatched types个:

error[E0308]: match arms have incompatible types
  --> src/main.rs:41:9
   |
41 | /         match self {
42 | |             Input::Console(ref c) => c.lines(),
   | |                                      --------- match arm with an incompatible type
43 | |             Input::File(ref f) => f.lines(),
44 | |         }
   | |_________^ expected enum `Input`, found struct `std::io::StdinLock`
   |
   = note: expected type `std::io::Lines<Input<'a>>`
              found type `std::io::Lines<std::io::StdinLock<'_>>`

我试着满足于:

match self {
    Input::Console(std::io::StdinLock(ref c)) => c.lines(),
    Input::File(std::io::BufReader(ref f)) => f.lines(),
}

... 但这也不管用.

看来我真的有点不知所措.