如何使錯誤鏈錯誤與失敗錯誤兼容？

Question

給出以下代碼：

extern crate dotenv; // v0.11.0
#[macro_use]
extern crate failure; // v0.1.1

#[derive(Debug, Fail)]
#[fail(display = "oh no")]
pub struct Error(dotenv::Error);

由於error-chain （v0.11，最新版本）不能保證其包裝錯誤是Sync （ 打開PR以解決問題 ），我收到一條錯誤消息，說明沒有為dotenv::Error實現Sync ：

error[E0277]: the trait bound `std::error::Error + std::marker::Send + 'static: std::marker::Sync` is not satisfied
 --> src/main.rs:5:17
  |
5 | #[derive(Debug, Fail)]
  |                 ^^^^ `std::error::Error + std::marker::Send + 'static` cannot be shared between threads safely
  |
  = help: the trait `std::marker::Sync` is not implemented for `std::error::Error + std::marker::Send + 'static`
  = note: required because of the requirements on the impl of `std::marker::Sync` for `std::ptr::Unique<std::error::Error + std::marker::Send + 'static>`
  = note: required because it appears within the type `std::boxed::Box<std::error::Error + std::marker::Send + 'static>`
  = note: required because it appears within the type `std::option::Option<std::boxed::Box<std::error::Error + std::marker::Send + 'static>>`
  = note: required because it appears within the type `error_chain::State`
  = note: required because it appears within the type `dotenv::Error`
  = note: required because it appears within the type `Error`

什么是最小量的樣板/工作，我可以讓這些類型很好地一起玩？ 我能想到的最簡單的事情就是添加一個ErrorWrapper newtype，這樣我就可以在Arc<Mutex<ERROR_CHAIN_TYPE>>上實現Error ：

use std::fmt::{self, Debug, Display, Formatter};
use std::sync::{Arc, Mutex};

#[derive(Debug, Fail)]
#[fail(display = "oh no")]
pub struct Error(ErrorWrapper<dotenv::Error>);

#[derive(Debug)]
struct ErrorWrapper<T>(Arc<Mutex<T>>)
where
    T: Debug;

impl<T> Display for ErrorWrapper<T>
where
    T: Debug,
{
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        write!(f, "oh no!")
    }
}

impl<T> ::std::error::Error for ErrorWrapper<T>
where
    T: Debug,
{
    fn description(&self) -> &str {
        "whoops"
    }
}

// ... plus a bit more for each `From<T>` that needs to be converted into
// `ErrorWrapper`

這是正確的方法嗎？ 對於那些不需要它的東西，是否會有更少的代碼/運行時成本轉換為Arc<Mutex<T>> ？

Answer 1

我唯一可以建議刪除Arc類型。

如果你有一些不是Sync東西然后換成Mutex類型，那么要將error-chain與failure集成，只需包裝dotenv::Error ：

#[macro_use]
extern crate failure;
extern crate dotenv;
use std::sync::Mutex;

#[derive(Debug, Fail)]
#[fail(display = "oh no")]
pub struct Error(Mutex<dotenv::Error>);

fn main() {
    match dotenv::dotenv() {
        Err(e) => {
            let err = Error(Mutex::new(e));
            println!("{}", err)
        }
        _ => (),
    }
}