Can’t implement Trait for &'a Trait when Trait is 'static

[chris-morgan]

Minimal example:

trait A: 'static { }
impl<'a> A for &'a A { }
fn main() { }

(&'a A can be written &'a (A + 'static) with the same outcome.)

<anon>:2:1: 2:25 error: declared lifetime bound not satisfied
<anon>:2 impl<'a> A for &'a A { }
         ^~~~~~~~~~~~~~~~~~~~~~~~
<anon>:2:1: 2:25 note: lifetime parameter instantiated with the lifetime 'a as defined on the impl at 2:0
<anon>:2 impl<'a> A for &'a A { }
         ^~~~~~~~~~~~~~~~~~~~~~~~
note: but lifetime parameter must outlive the static lifetime
error: aborting due to previous error

Sure, A itself must be 'static, but that shouldn’t prevent the creation of a non-static reference to A.

[huonw]

cc @nikomatsakis, seems that the constraints may be backwards? (The compiler should be checking that 'static outlives 'a?)

[pnkfelix]

I am not sure this is a bug. cc @nikomatsakis removing nomination tag.

[huonw]

Looking at it now, I agree it's not a bug: the 'static bound on A means anything you implement A for needs to satisfy 'static, but &'a A does not, so the problem is writing impl<'a> A for &'a ..., not just writing &'a A itself.

[nikomatsakis]

Right, not a bug.