in reply to Re^9: Common Perl Pitfalls
in thread Common Perl Pitfalls

But if done right it's 1 compilation versus 12 compilations and 20 stringifications over the whole runtime of the script! According to the first of your benchmarks about 1 millisecond of difference. Huge deal indeed!

If your regexes grow way too big, do whatever you must. Under normal conditions the difference in negligible, while the fact that I don't have to worry whether I'm writing a regexp or a single quoted string that will eventually happen to be part of a regexp is not. Even though or rather just because the difference is slight and changes the behaviour rarely.

Jenda
Enoch was right!
Enjoy the last years of Rome.

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Re^11: Common Perl Pitfalls
by JavaFan (Canon) on Apr 11, 2012 at 23:36 UTC
    For me, it's the other way around. For the majority of the (sub)patterns (even with most uses of backslashes), it doesn't matter whether you write q{PAT} or qr{PAT} (it's the same keystrokes inside the braces). Meaning, there's absolutely nada difference in readability.

    Why go for the expensive solution? If your pattern grows, at what moment do you revisit your program, and chop off the r in qr?

    It's not that I never use qr. Sometimes, there's a (sub)pattern that's more readable as qr than as q. And sometimes, one does want a first class regexp construct. But those are the exceptions.

    Do note that using q building blocks to build your patterns gives you more flexibility than limiting yourself to just qr: 

    my $vowels = 'aeiou';
my $odds = '13579';
my $odd_or_vowel = '[$vowels$odds]';

    [download]
    To write that as qr, you'd have to write something like: 
    my $vowels = qr/[aeiou]/;
my $odds = qr/[13579]/;
my $odd_or_vowel = qr/$vowels|$odds/;

    [download]
    which, while matching the same language, throws off the optimizer, and makes not only for a slower compilation, the match itself is slower.
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