如何为所有现有错误实现错误包装器? [英] How to implement an error wrapper for all existing Errors?

问题描述

我想在所有函数中使用我自定义的错误类型，我需要包装现有的标准错误，以便 ? 运算符会成功.

I want to use my customised error type in all functions and I need to wrap the existing standard errors so that the ? operator will succeed.

这是我正在做的:

use std::{error::Error, fmt, fs};

#[derive(Debug)]
enum MyError {
    A,
    B,
}

impl fmt::Display for MyError {
    fn fmt(&self, _f: &mut fmt::Formatter) -> fmt::Result {
        Ok(())
    }
}

impl Error for MyError {
    fn description(&self) -> &str {
        ""
    }
}

trait NotMyError {}

impl<T: NotMyError + Error> From<T> for MyError {
    fn from(_: T) -> MyError {
        MyError::A
    }
}

fn test() -> Result<(), MyError> {
    fs::read_dir("test")?;
    Ok(())
}

fn main() {}

编译器抱怨:

error[E0277]: the trait bound `std::io::Error: NotMyError` is not satisfied
  --> src/main.rs:30:5
   |
30 |     fs::read_dir("test")?;
   |     ^^^^^^^^^^^^^^^^^^^^^ the trait `NotMyError` is not implemented for `std::io::Error`
   |
   = note: required because of the requirements on the impl of `std::convert::From<std::io::Error>` for `MyError`
   = note: required by `std::convert::From::from`

推荐答案

一篇关于它.要为您的错误获得一流的支持，您需要做两件事:

There's an excellent post about it. To get first-class support for your error you need to do two things:

• 实现Error trait 适合您的类型.
• 为要与 ? 运算符(quick_error crate 有助于自动执行此操作.

• Implement the Error trait for your type.
• Implement std::convert::From for error types you want to use seamlessly with the ? operator (the quick_error crate helps automate this).

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