为什么失败::失败特性绑定不满足我的结果类型别名

Question

我正在尝试实现事件挂钩，如"Rust中的简单事件挂钩"所示，同时也使用故障机箱的Error+ErrorKind模式。

这是我代码的精简版本：

#[macro_use]
extern crate failure;
use failure::{Backtrace, Context, Error, Fail};
use std::fmt;
#[derive(Debug)]
pub struct PortalError {
inner: Context<PortalErrorKind>,
}
impl Fail for PortalError {
fn cause(&self) -> Option<&Fail> {
self.inner.cause()
}
fn backtrace(&self) -> Option<&Backtrace> {
self.inner.backtrace()
}
}
impl fmt::Display for PortalError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Display::fmt(&self.inner, f)
}
}
#[derive(Copy, Clone, PartialEq, Debug, Fail)]
pub enum PortalErrorKind {
#[fail(display = "Unknown Error")]
Unknown,
}
//----------------------------------------------------------
pub type PortalResult<T> = Result<PortalError, T>;
pub trait Portal {
fn get_something(&self) -> PortalResult<Vec<u32>>;
}
//----------------------------------------------------------
pub trait FeedApi<'a> {
type T: FeedApi<'a>;
fn new<P: Portal + 'a>(portal: P) -> Result<Self::T, Error>;
}
//----------------------------------------------------------
pub struct Feedly<'a> {
portal: Box<Portal + 'a>,
}
impl<'a> FeedApi<'a> for Feedly<'a> {
type T = Feedly<'a>;
fn new<P: Portal + 'a>(portal: P) -> Result<Self::T, Error> {
Ok(Feedly {
portal: Box::new(portal),
})
}
}
impl<'a> Feedly<'a> {
pub fn demo_function(&self) -> Result<(), Error> {
let _ = self.portal.get_something().context(PortalErrorKind::Unknown)?;
Ok(())
}
}
fn main() {
println!("Hello, world!");
}

[dependencies]
failure = "0.1.1"

在"Feedly"的方法中，我想使用门户：

self.portal.get_something().context(PortalErrorKind::Unknown)?

但我得到以下错误：

error[E0599]: no method named `context` found for type `std::result::Result<PortalError, std::vec::Vec<u32>>` in the current scope
--> src/main.rs:67:45
|
67 |         let _ = self.portal.get_something().context(PortalErrorKind::Unknown)?;
|                                             ^^^^^^^
|
= note: the method `context` exists but the following trait bounds were not satisfied:
`std::result::Result<PortalError, std::vec::Vec<u32>> : failure::Fail`
`&std::result::Result<PortalError, std::vec::Vec<u32>> : failure::Fail`
`&mut std::result::Result<PortalError, std::vec::Vec<u32>> : failure::Fail`

通过查阅文档，failure::Fail特征具有绑定的'static。并且方法CCD_ 5具有绑定的CCD_。

我不确定哪种特质在这里不满足。装箱的Portal既不是Sized也不是'static，但返回的结果应该是，对吧？

这是我第一次在Rust中处理盒子和生命。

Answer 1

pub type PortalResult<T> = Result<PortalError, T>;

Result有两个类型参数：成功类型和错误类型。你把它们调换了位置；你想要：

pub type PortalResult<T> = Result<T, PortalError>;