Re: Speed comparison of regex versus index, lc, and / /i


Quoth abigail@xxxxxxxxxx:
Ben Morrow (ben@xxxxxxxxxxxx) wrote on VCCCLXXXVII September MCMXCIII in
<URL:news:mas6h5-nt11.ln1@xxxxxxxxxxxxxxxxxxxxxxx>:
""
"" Note that m// will only use the precompiled form of the qr// if the
"" $rx is the only thing in the match. Something like /^$rx/ or
"" /$rx1|$rx2/ or even / $rx/x will cause the regex to be recompiled
"" every time all over again.

That hasn't been the case for over a decade or so:

perl -Mre=debug -wE '$re = qr /foo/;
for (qw [bar baz]) {/ $re/}' 2>&1| grep '^Compiling'
Compiling REx "foo"
Compiling REx " (?-xism:foo)"

It only compiles twice, once for the qr //, and once for the m //.

You know, I did actually test that :).

~% perl -Mre=debug -e'$qr=qr/a/; /$qr/' 2>&1 | grep Comp
Compiling REx `a'
~% perl -Mre=debug -e'$qr=qr/a/; / $qr/x' 2>&1 | grep Comp
Compiling REx `a'
Compiling REx ` (?-xism:a)'

If it's actually using the compiled form of the qr//, it doesn't need to
compile for the m// at all. The fact your example only compiles the m//
once is the 'if a variable hasn't changed, don't recompile'
optimization, which applies regardless of qr//:

~% perl -Mre=debug -e'$qr=qr/a/; / $qr/ for 1, 2' 2>&1 | grep Comp
Compiling REx `a'
Compiling REx ` (?-xism:a)'
~% perl -Mre=debug -e'$qr=q/a/; / $qr/ for 1, 2' 2>&1 | grep Comp
Compiling REx ` a'

Out of obfuscated code, I would never use /o.

Me either.

Ben

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