fn is no longer cloneable about iron HOT 12 CLOSED

This is a serious problem. We have a lot of existing code that relies on fn's being Cloneable.

from iron.

Unless you want to pair on rust-lang/rust, I'm not sure we have a recourse.

from iron.

huon mentioned that the recent break was probably due to this: rust-lang/rust#15191

from iron.

This seems outside of our ability to fix.

I'm going to create a FromFn struct, which would be usable like so:
server.chain.link(FromFn::new(hello_world_fn))

from iron.

Putting it in iron::middleware::FromFn

from iron.

I don't think we should do this. It still involves changing our code at every point where a bare function was used, so the overhead is the same as just impl'ing a function as fn enter in a middleware struct, but it introduces a lot of technical debt (and what might be considered code bloat). I commented on this strategy when I opened this issue.

Can you come back to discuss this?

from iron.

I noticed you handle this issue like this:

fe36c2d

Do you have any insight in how this will be handled upstream? I mean, is it intended that fn is no longer clonable or is this a bug that should be resolved soon?

from iron.

We aren't sure. We think it's a bug with trait detection related to some new logic in the compiler for type checking traits.

FromFn is intentionally bare-bones so it can be easily deleted when this gets resolved.

from iron.

It should be fixed eventually. There's an active issue out on it - rust-lang/rust#14820.

The plan is to fix it with impl<T:Copy> Clone for T { ... } (stated in the above issue).
(I don't really understand why this isn't possible already, but according to the issue it's not.)

from iron.

Ah, I see. Thanks for the pointers!

from iron.

@zzmp it's impossible right now because if you have a generic impl for a trait you can't have any other impls for that trait, which is a known issue.

Basically, if you had impl<T: Copy> Clone for T { fn clone(&self) -> T { *self } } then you couldn't impl Clone for any type that wasn't already Copy which is basically the entire point.

This is also why we have impl Middleware for Box<Chain> instead of impl<C: Chain> Middleware for C.

from iron.

@reem don't make my head spin ;-)

from iron.