Allow custom `dyn` traits with non-static lifetime

[srid]

Instead of dyn Any I'd like to iterate over dyn MyTrait (dyn Checkable in the example below) with the assumption that all fields in the struct implement that trait (else, there should be a compile error).

Example

pub struct NixHealth {
    pub max_jobs: MaxJobs,
    pub caches: Caches,
    pub flake_enabled: FlakeEnabled,
    pub min_nix_version: MinNixVersion,
    pub trusted_users: TrustedUsers,
}

Manual implementration

impl<'a> IntoIterator for &'a NixHealth {
    type Item = &'a dyn Checkable;
    type IntoIter = std::vec::IntoIter<Self::Item>;

    fn into_iter(self) -> Self::IntoIter {
        let items: Vec<Self::Item> = vec![
            &self.min_nix_version,
            &self.flake_enabled,
            &self.max_jobs,
            &self.caches,
            &self.trusted_users,
        ];
        items.into_iter()
    }
}

Code in context: https://github.com/juspay/nix-browser/blob/913c505d501efd15beff7388404d9a7f4e4e4c58/crates/nix_health/src/lib.rs#L24-L48

[kaimast]

I agree. Would love to be able to use ToString for my specific use case.