BeforeMiddleware 实现需要 core::ops::Fn 实现

Question

我正在尝试为我拥有的 struct 实现 BeforeMiddleware 特性。我写了下面的代码：

impl BeforeMiddleware for Auth {
    fn before(&self, _: &mut Request) -> IronResult<()> {
        println!("before called");
        Ok(())
    }

    fn catch(&self, _: &mut Request, err: IronError) -> IronResult<()> {
        println!("catch called");
        Err(err)
    }
}

我收到以下错误：

> cargo build
...
src/handlers/mod.rs:38:11: 38:28 error: the trait `for<'r, 'r, 'r> core::ops::Fn<(&'r mut iron::request::Request<'r, 'r>,)>` is not implemented for the type `auth::Auth` [E0277]
src/handlers/mod.rs:38     chain.link_before(auth);
                                 ^~~~~~~~~~~~~~~~~
src/handlers/mod.rs:38:11: 38:28 help: run `rustc --explain E0277` to see a detailed explanation
src/handlers/mod.rs:38:11: 38:28 error: the trait `for<'r, 'r, 'r> core::ops::FnOnce<(&'r mut iron::request::Request<'r, 'r>,)>` is not implemented for the type `auth::Auth` [E0277]
src/handlers/mod.rs:38     chain.link_before(auth);
                                 ^~~~~~~~~~~~~~~~~
src/handlers/mod.rs:38:11: 38:28 help: run `rustc --explain E0277` to see a detailed explanation
error: aborting due to 2 previous errors
...

但是 the documentation 说 link_before 函数只需要 BeforeMiddleware。

有谁知道我为什么会看到这个错误以及如何解决它？

编辑：

我实际上使用的是静态 auth，在将其设为非静态后问题就消失了。

Answer 1

这很好用：

extern crate iron;

use iron::{Chain, BeforeMiddleware, IronResult, Request, Response, IronError};
use iron::status;

struct Auth;

impl BeforeMiddleware for Auth {
    fn before(&self, _: &mut Request) -> IronResult<()> {
        println!("before called");
        Ok(())
    }

    fn catch(&self, _: &mut Request, err: IronError) -> IronResult<()> {
        println!("catch called");
        Err(err)
    }
}

fn main() {
    fn hello_world(_: &mut Request) -> IronResult<Response> {
        Ok(Response::with((status::Ok, "Hello World!")))
    }

    let mut c = Chain::new(hello_world);
    let auth = Auth;
    c.link_before(auth);
}

这是针对 iron 0.2.6 编译的。

BeforeMiddleware 实现需要 core::ops::Fn 实现

BeforeMiddleware implementation requires core::ops::Fn implementation

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