public List<TensorFunction<NAMETYPE>> selectorFunctions() {
        var result = new ArrayList<TensorFunction<NAMETYPE>>();
        for (var dimVal : subspaceAddress) {
            dimVal.index().flatMap(ScalarFunction::asTensorFunction).ifPresent(result::add);
        }
        return result;
    }
Creates a value function

@param argument the tensor to return a cell value from
@param subspaceAddress a description of the address of the cell to return the value of. This is not a TensorAddress
                       because those require a type, but a type is not resolved until this is evaluated
vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java