BeforeMiddleware implementation requires core::ops::Fn implementation

问题

I am trying to implement the BeforeMiddleware trait for a struct I have. I have written the following code:

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)
    }
}

I am getting the following error:

> 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
...

But the documentation says the link_before function requires a BeforeMiddleware only.

Does anyone know why I am seeing this error and how to fix it?

EDIT:

I was actually using a static auth, after making it non-static the problem went away.

回答1:

This works just fine:

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);
}

This compiles against iron 0.2.6.

来源：https://stackoverflow.com/questions/34489422/beforemiddleware-implementation-requires-coreopsfn-implementation

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