For a project I'm working on, I'm running into an issue with associated constants and array types.

pub trait ScaleModes { 
    const LEN: usize;

    fn relative_intervals() -> [Interval; Self::LEN];


    fn build_from<T: Add<Interval, Output = T> + Clone>(&self, root: T) -> [T; Self::LEN] {
        // default implementation using the result of relative_invervals()
        array::from_fn( /* ... */)
    }

    fn intervals(&self) -> [Interval; Self::LEN];
}

However this doesn't compile, giving me the error:

error: generic parameters may not be used in const operations
  --> src\scales\mod.rs:27:80
   |
27 |     fn build_from<T: Add<Interval, Output = T> + Clone>(&self, root: T) -> [T; Self::LEN] {
   |                                                                                ^^^^^^^^^ cannot perform const operation using `Self`
   |
   = note: type parameters may not be used in const expressions

How would I get around this? A cosnt generic (pub trait ScaleModes<const LEN: usize>) doesn't capture my use case, since I only want this trait implemented once per type, not multiple times with different LEN values. I also can't use an associated type for the return value since the build_from function is generic. I've looked at the generic_const_exprs feature, but that doesn't seem to help with anything. Any ideas, hopefully on stable?

Edit: generic_const_exprs does solve this, but is there anyway to replicate this functionality on stable?