There is no way to `unsafe impl` `'static`

[reem]

This would be extremely useful when using invariant lifetimes as a marker for e.g. safe unchecked indexing, it would be nice to be able to say unsafe impl<'id> 'static for InvariantLifetime<'id> {} (where InvariantLifetime<'a> is PhantomData<fn(&'a ()) -> &'a ()>).

[reem]

I am not sure if this is at all feasible, if it's completely bonkers feel free to close.

[huonw]

This feels somewhat crazy, but it'd be oh-so-useful: I've had to box things behind trait objects just so that I can erase the lifetime (transmuting Box<Trait + 'a> to Box<Trait + 'static>) for cases when I'm guaranteeing lifetime correctness in some external way.

cc @rust-lang/lang

[reem]

If we had 'anonymous/injected type parameter which doesn't unify with anything but itself' as a native part of the type system, it would also solve this problem (using lifetimes for this is admittedly a hack).

[huonw]

That solves using lifetimes as a tag, but not having to (ab)use trait objects to force things to be 'static (unlike the marker traits).

[arielb1]

This is currently dangerous because rustc assumes that every lifetime that is :'static equals 'static. Also, this would be very dangerous with Any.

[aturon]

The lang team discussed this issue, and felt that while there are plausible motivations for the feature, there are also significant dangers. We would consider a fleshed out RFC in this area presenting a strong argument for the importance of the feature and mitigation of the pitfalls that have been raised here.