What interface bugs have you ran into in the ecosystem?

General Usage
12

I don’t really understand this one for a few reasons:

  • Dispatching a method on interfaces as if they were types (the supertype of all iterators being a not very helpful Any) will cause brittle ambiguity issues like multiple supertypes would. Multiple Holy traits evade such issues by dedicating a trait function to check each trait set, and you can only have 1 trait per set. The trait function call follows type-based dispatch, so traits are not independent of types or dispatch limitations.
  • Assuming you’re not talking about the iteration-reliant last(x, n) methods, last(x) depends on lastindex, which is part of the indexing interface, not the iteration interface. Those often come together but you can have either alone.
  • How would a fallback last even work for iterators or indexables? Neither necessarily have a last element and could need to error upon a last(x) call, which will just work if lastindex isn’t implemented for the concrete type. The only change I could see interface/trait dispatch make is turning a MethodError for lastindex into a MethodError for last.
  • Upon rereading, it is clearer that you intended to implement a last method for iterables in addition to the method for indexables, and neither needs to be always successful. Unfortunately, dispatching on multiple orthogonal interfaces would have the same ambiguity issues as multiple supertypes, for example does an iterable and indexable input dispatch the call to the iterable method or the indexable method? The approach that comes to mind is to modify the existing method to check for the quicker indexing sense of last element then the slower iteration sense of last element (which has the HasLength and HasShape{N} traits of the IteratorSize trait set). I think this could be done by checking hasmethod on lastindex+getindex then length+iterate, and if Tricks.jl is right, this can occur at compile-time and be invalidated by method changes in v1.10. I have not verified this behavior or applicable’s, nor do I know exactly what builtins, intrinsics, and tfuncs are.