I was trying to point out that "the overhead of looking up the key, dereferencing the value," is marginal relative to the overhead of "executing the code ref".

Even that last phrase slightly conflates

• the process of invoking the sub;
• executing the code it contains.

I realise that you know the difference, but your wording--combined with your use of "purported"--tended to imply that "looking up the key" was a significant factor. Which it isn't. I sought to demonstrate this.

Unfortunately, typical dispatch tables use code refs.

It wouldn't be a dispatch table if it didn't :). I agree, you cannot avoid the overhead of calling the subroutine.

I had a couple of cracks at coding a 'macro processor'--really just a sub inliner a couple of years ago.one of them may even be posted here somewhere?--using source filters, but it was never very satisfactory.