Support derive for types with const generics

[dtolnay]

This has not landed in nightly yet but is being tracked in rust-lang/rust#44580.

It would be good to begin thinking about how to form the right trait bounds for such types.

#[macro_use]
extern crate serde_derive;

#[derive(Serialize, Deserialize)]
struct S<T, const N: usize> {
    array: [T; N],
}

[dtolnay]

Will reopen if the implementation in the compiler ever lands and we start hearing use cases.

[JulianKnodt]

Hi, I hope it's ok that I'm commenting on an older thread, but I was wondering if this was being revisited now that const-generics are available on nightly?

The main use case for const-generics would probably be in numerical applications, so I can see the main use case serving a similar role to numpy's .npy or .npz format.

If there is anything I can do to implement this let me know!

[vadixidav]

I second this as I would like to switch the hnsw crate to const generics in preparation for its stabilization. Having a feature that enabled those impls would be beneficial. Alternatively, serde could automatically detect if it is on a compatible nightly rust version using select-rustc and enable the const generics impls in that case.

[Kromey]

Const generics have landed in stable now, and as I noted in the above linked issue I cannot currently derive Serde traits because I use this feature. While I can probably work around it via the try_from and into attributes, having the ability to derive them instead would greatly simplify the task.

[TehPers]

I believe this issue was reopened in #1937. I'm also looking forward to this being implemented in the future.