Too new for this world problem when called from a function

Indeed. I was putting them in the wrong place. If I introduce them into the stag_compute, it works. It looks like this:

  function stag_compute(s :: Stag)                                               
    println(Base.invokelatest(s.b.value, 1.0, 1.0, 1.0))                                   
  end

But, as the Julia documentation writes: “The drawback is that invokelatest is somewhat slower than calling f directly, and the type of the result cannot be inferred by the compiler.” I could live with the “somewhat slower”, but don’t fancy the fact that " the type cannot be inferred by the compiler"