Unity Mono AOT iOS failure for generic method

Hi there.

We're bumping into AOT limitations of Mono. Basically we have this:

 Attempting to JIT compile 'com.tinylabproductions.TLPLib.Functional.Option:fold<com.tinylabproductions.TLPLib.Functional.Try`1<com.tinylabproductions.TLPLib.Formats.SimpleJSON.JSONClass>, bool> (com.tinylabproductions.TLPLib.Functional.Option`1<com.tinylabproductions.TLPLib.Functional.Try`1<com.tinylabproductions.TLPLib.Formats.SimpleJSON.JSONClass>>,System.Fn`1<bool>,System.Fn`2<com.tinylabproductions.TLPLib.Functional.Try`1<com.tinylabproductions.TLPLib.Formats.SimpleJSON.JSONClass>, bool>)' while running with --aot-only.

Which looks a bit horrible. :)

Fold was defined as:

 interface Option<out A> {
   B fold(Fn<B> ifEmpty, Fn<A, B> ifSome);
 }

Fn is a delegate type we have defined:

 public delegate R Fn<in P1, out R>(P1 p1);

However upon reading http://www.reentrygames.com/unity-3d-using-extension-methods-to-solve-problems-with-generics-and-aot-on-ios/ I've tried changing all generic interface calls to static extension methods like:

 public static class Option {
   public static B fold<A, B>(
     this Option<A> opt, Fn<B> ifEmpty, Fn<A, B> ifNonEmpty
   ) {
     return opt.isDefined ? ifNonEmpty(opt.get) : ifEmpty();
   }
 }

However AOT is still not picking it up. The call site looks like:

   public interface Promise<in A> {
     /** Complete with value, return false if already completed. **/
     bool tryComplete(Try<A> v);
   }

 class FutureImpl<A> : Future<A>, Promise<A> {
     private Option<Try<A>> _value = F.none<Try<A>>();
 
     public bool tryComplete(Try<A> v) {
       // FOLD FAILS HERE.
       var ret = value.
         fold(() => { _value = F.some(v); return true; }, _ => false);
       completed(v);
       return ret;
     }
 }
 
   public interface Try<out A> { ... }

I was wondering if you guys bumped into this and perhaps could share tips and tricks to work around this. Or have you ditched generics all together?

Thanks a lot!