Why Value is pub while its bound Sealed is sealed?

[tisonkun]

pub trait Value: crate::sealed::Sealed {
    /// Visits this value with the given `Visitor`.
    fn record(&self, key: &Field, visitor: &mut dyn Visit);
}

mod sealed {
    pub trait Sealed {}
}

I don't see a solution to implement Value in application code. I can see that it is possible using DebugValue or other out-of-the-box implementation for boxing the value, but why Value is pub while its bound Sealed is sealed?

[hawkw]

Value is not intended to be implemented in user code, that's why it's Sealed. It's only implemented for certain Rust primitive types. The intention is to replace the current value system with a more sophisticated implementation that allows user code to implement Value for arbitrary types, but this will require some significant changes to the trait. Until then, the trait has been sealed to prevent downstream implementations that would be broken by those changes.

However, the trait must be used in user code. Therefore, it has to be pub. pub traits bounded with Sealed allow traits to be used publicly while preventing downstream implementations. See https://rust-lang.github.io/api-guidelines/future-proofing.html#sealed-traits-protect-against-downstream-implementations-c-sealed

[tisonkun]

Thanks for your detailed answer and I just notice that we have a Discussion forum.

[rollo-b2c2]

Is there any reason this is still sealed? It's kinda annoying to be honest, if it breaks it breaks.

I'm happy to pin my tracing version. It has all the features I want. If there's a new feature and it breaks I can weigh up if the time invested in porting it.

[davidbarsky]

Because the successor to Value is valuable. You can enable it today, if you'd like: https://docs.rs/tracing/latest/tracing/#unstable-features.