ForwardDiff.jl support?

[longemen3000]

is it possible to add ForwardDiff.jl support as an extension? i can help if it's necessary

[Expander]

That's a good idea! How would that support look like? Would we have to provide additional overloads?

Now that you're asking, I'm wondering if there is a way to also support other differentiation libraries? Do you know if there is a generic way to support all of them?

[longemen3000]

For ForwardDiff yes, you would need to support overloads, I can make a PR with the corresponding changes to allow support.
For the rest of AD libraries, I think you only need to support ChainRules.jl. Most of the AD libraries in Julia take ad rules using ChainRules. There is also Enzyme.jl, but Ive never written overloads for that package.

The way to support this is via the pkg extension mechanism (from Julia 1.9 onwards). This allows to only load the AD code if it's necessary

[Expander]

A PR would be great! Could you please also add corresponding tests?

One question, though: Would this PR require to add a dependency? I'm asking, because I'd like to avoid this as much as possible. (A "dev"-dependency in the [extras] section would be no problem.)

[longemen3000]

The extension mechanism does not require direct dependencies (in partícular they are weak dependencies, added in the [weakdeps] section). Check this :https://julialang.org/blog/2023/04/julia-1.9-highlights/#package_extensions