I think that this observation is not as relevant to the task at hand that it seems. The author is in the same position as the implementor of a VM, who has to de

I think that this observation is not as relevant to the task at hand that it seems. The author is in the same position as the implementor of a VM, who has to decide which operation will be a primitive and which will not be. What is actually more important than anything else if you care about performance is which operations are likely to be called from hot loops. It's classic optimization wisdom except that you can only work on expected scenarios rather than real-world uses (until you release your stuff and other people use it). So a 100x slower abstraction is ok(-ish) as long as it's not somthing to be used in performance critical sections.