If you annotate your Rust function with the #[rzf::rzf] attribute, how can you call it from your ObjectScript code? The presentation slides were a little cut off in the video so I can't see that part.

I do have the source, and I ended deleting and recreating the class from it.

You only need to install this in one place, in the last method or routine call in your call stack. If your stack is like this AAA -> BBB -> CCC^ABC -> XXX^XYZ, then you need to put Stuart's code in a method called by XXX^XYZ

For example, assume you have these classmethods

ClassMethod GrandParent()
{
    do ..Parent()
}
ClassMethod Parent()
{
    do ..Child()
}
ClassMethod Child()
{
    do ..Inspector()
}
ClassMethod Inspector()
{
    FOR i=0:1:$STACK(-1)-1 {
      SET s=$STACK(i,"PLACE")
      SET retloc=$PIECE(s," ")
      TRY { SET code=$TEXT(@retloc) } CATCH { SET code="n/a" }
      WRITE !,retloc," (",$PIECE(s," ",2),") -> ",code
    }
}

Then if you call GrandParent(), then it will print this:

@ (+1) -> n/a
GrandParent+1^Sample.Test.1 (+1) ->     do ..Parent() }
Parent+1^Sample.Test.1 (+1) ->     do ..Child() }
Child+1^Sample.Test.1 (+1) ->     do ..Inspector() }