A #rustlang feature I often want to reach for: an #[unimplemented] attribute I can put on functions that lets me set up the function signature but results in an error if called from a function that is also not marked similarly. This would be really useful for sketching out the design of a future API without needing to commit to it today, or run the risk of a dependent crate accidentally relying on its existence if its body is unimplemented!().
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@jsbarretto
Would it work to put the code in a new feature of your crate, combined with todo!() in the bodies?
Features allow for conditional compilation:
@KingmaYpe Yeah, I often end up adding an `unstable` feature to the crates I maintain with an explicit, documented semver exception for anything that falls behind it. I'm not quite sure this is what I'm looking for though: I'd rather see something that the type system is aware of.
@jsbarretto Not totally the same thing, but I tend to create functions in Go that only and always return a `NotImplemented` error and a zero value.
I can get the shape of the program/library the way I want it and even write always-failing tests to get rolling.
As I say, not the same thing -- but I can see how this attribute would be nice.
@fm2279 Rust has the `unimplemented!()` macro which effectively does the same thing: panics, with a backtrace. But I'm looking for something that allows sketching out an API in a production environment without having users accidentally rely on it.
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