Question

我在使用try!和?宏时遇到了极大的困难，以至于我开始质疑现实的结构。我举起了straight from the rust-docs以下的例子，它仍然在我的脸上爆炸。

代码：

pub use std::fs::File;
pub use std::io::prelude::*;

fn main() {
    let mut file: File = File::open("foo.txt")?;
    file.write_all(b"Hello, world!")?;
}

错误：

error[E0277]: the trait bound `(): std::ops::Try` is not satisfied
--> src/main.rs:6:23
|
6 |     let mut file: File = File::open("foo.txt")?;
|                          ----------------------
|                          |
|                          the trait `std::ops::Try` is not implemented for `()`
|                          in this macro invocation
|
= note: required by `std::ops::Try::from_error`

error[E0277]: the trait bound `(): std::ops::Try` is not satisfied
--> src/main.rs:7:2
|
7 |     file.write_all(b"Hello, world!")?;
|     ---------------------------------
|     |
|     the trait `std::ops::Try` is not implemented for `()`
|     in this macro invocation
|
= note: required by `std::ops::Try::from_error`

根据rustup（1.19.0）

，我正在使用Rust的最新稳定版本

Answer 1

目前预计这些示例将在包含Result的函数中运行;如果单击示例右上角的“运行”，您将看到它扩展为：

fn main() {
    use std::fs::File;
    use std::io::prelude::*;

    fn foo() -> std::io::Result<()> {
        let mut file = File::create("foo.txt")?;
        file.write_all(b"Hello, world!")?;
        Ok(())
    }
}

这是因为返回Result的函数（如File::create和io::Write::write_all）应该考虑到可能的错误（在文档示例中尤为重要）。

有一个RFC允许从Result返回main()已经合并的?，main()允许<div id="app"> <input type="text" v-model="model1" /> </div> <div> <div id="model2">ABCDEFG</div> <input type="text" /> </div> <script> new Vue({ el: '#app', data: {'model1': 'value'}, ... ... ... }); </script>在primary-expression }仍然有效。

带问号的std文档示例无法编译

1 个答案: