You were shown an example of exactly why this thinking is incorrect but you still insist...
Also, it's trivial to keep Ken's implementation as the slow path. If request patterns change, dig up the new fast path and put the old one in Ken's slow path code. Most of the performance will still come from the initial `if`.
It’s ungenerous to assume I would be against the if statement + Ken’s. But Ken’s approach is critically important and the “if” statement should just be a 1 entry cache instead of being hard coded. Getting this stuff right in a future proofed durable way is actually quite hard even when you notice the opportunity.
Also, it's trivial to keep Ken's implementation as the slow path. If request patterns change, dig up the new fast path and put the old one in Ken's slow path code. Most of the performance will still come from the initial `if`.