This is a good question. The answer is that the REx engine does not optimize \d{2} into \d\d.

Here's how to check: 

[~] $ perl -Mre=debug -e'qr/\d{2}/'
Freeing REx: `,'
Compiling REx `\d{2}'
size 4 first at 3
   1: CURLY {2,2}(4)
   3:   DIGIT(0)
   4: END(0)
stclass `DIGIT' minlen 2 
Freeing REx: `\d{2}'
[~] $ perl -Mre=debug -e'qr/\d\d/'
Freeing REx: `,'
Compiling REx `\d\d'
size 3 first at 1
   1: DIGIT(2)
   2: DIGIT(3)
   3: END(0)
stclass `DIGIT' minlen 2 
Freeing REx: `\d\d'

[download]

Why doesn't it? I don't know. But as the Benchmarks above have noted, I can't imagine that difference being notable enough to really worry about.

-dlc

In reply to RE: Regex optimizations by dchetlin
in thread Regex optimizations by Ovid

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