I too am a huge fan of qr;

Ehrrmm, I see that you hardly need a lesson in how to use qr. :)

however, I think this situation is a perfect use of the /o operator.

I don't, especially since it doesn't work on ActivePerl. :) But there's also another reason why I don't like to use it. As I've already said here perl optimizes away recompilation in simple cases like this. As your benchmark shows there's not much difference between with and without the o modifier. So in this case I'd prefer not using it. And the reason for that is that I'm scared of myself. One day I might put the code in a subroutine. Another day I might change it to take arguments that I use in the regex. If I forget about the o -- and I most probably will -- it might take me a while to discover the bug. If I use qr for this, or even nothing fancy at all, I won't get bitten.

I code with a lot of personal style and hints, and for me the o says "this is a dynamically set constant, and is supposed to be that way, so don't bother. It should never change. NEVER!". Often I don't mean that, and hence I use qr instead. I'm scared of my own benchmark results though: (your code)

Benchmark: timing 1000 iterations of None, Slasho, qr...
  None: 30 wallclock secs (30.08 usr + 0.14 sys = 30.22 CPU) @ 33.09/s
Slasho: 29 wallclock secs (28.74 usr + 0.02 sys = 28.76 CPU) @ 34.77/s
    qr: 31 wallclock secs (30.49 usr + 0.00 sys = 30.49 CPU) @ 32.80/s
[download]

For me qr is even worse. This does indeed surprise me.

Cheers,
-Anomo