Question

我正在尝试使用readline驱动的命令提示符创建一个程序。

我正在使用this crate。

readline = "0.0.11"

这是存储库中的示例。（链接到存储库位于包装箱的页面上。）

#![cfg(not(test))]

extern crate readline;

use readline::readline;

use std::ffi::CString;
use std::io::Write;
use std::io;

fn main() {
    let prompt = CString::new("user> ").unwrap();
    let mut stdout = io::stdout();
    while let Ok(s) = readline(&prompt) {
        stdout.write_all(s.to_bytes()).unwrap();
        stdout.write_all(b"\n").unwrap();
    }
    stdout.write_all(b"\n").unwrap();
}

我正在尝试将s从readline::common::ReadlineBytes转换为std::string::String，因此我可以match就这样。

while let Ok(s) = readline(&prompt){
    let command = str::from_utf8(&s.to_bytes()).unwrap();
    match command {
        "exit"  => std::process::exit,
        "again" => break,
        _ => println!("error")
    }
    println!("{}", command);
}

但我一直收到这个错误：

main.rs:18:9: 22:10 error: match arms have incompatible types:
 expected `fn(i32) -> ! {std::process::exit}`,
    found `()`
(expected fn item,
    found ()) [E0308]
main.rs:18         match command {
main.rs:19             "exit"  => std::process::exit,
main.rs:20             "again" => break,
main.rs:21             _ => println!("error")
main.rs:22         }
note: in expansion of while let expansion
main.rs:16:5: 24:6 note: expansion site
main.rs:18:9: 22:10 help: run `rustc --explain E0308` to see a detailed explanation
main.rs:21:18: 21:35 note: match arm with an incompatible type
main.rs:21             _ => println!("error")
                            ^~~~~~~~~~~~~~~~~
note: in expansion of while let expansion
main.rs:16:5: 24:6 note: expansion site
error: aborting due to previous error

Answer 1

匹配武器都必须返回相同的类型。再次查看您的错误消息：

main.rs:18:9: 22:10 error: match arms have incompatible types:
 expected `fn(i32) -> ! {std::process::exit}`,
    found `()`
(expected fn item,
    found ()) [E0308]

你的一个匹配臂正在返回()，另一个正在返回类型fn(i32) -> ! {std::process::exit} - 一个函数。

看看你的代码：

"exit"  => std::process::exit,

您不是致电 exit，您只是返回对它的引用。

将readline的ReadlineBytes转换为字符串

1 个答案: