Re^2: ??{ } oddity

ah ok, thanks!

a friend of mine asked me this question (well, actually he asked how he could execute a piece of code, well actually call a method, in a m//. i made the method return a static value, but it will mostly likely do something else..)

he gave me a theoretical example of what he was trying... so i don't really know what his intentions were. I just found the ??{ } expression in perldoc perlre.

but thanks for the answer, i understand the behaviour now

to ask a question is a moment of shame
to remain ignorant is a lifelong shame

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Re^3: ??{ } oddity by Roy Johnson (Monsignor) on Apr 28, 2005 at 15:54 UTC
A regex is a double-quote-ish expression, so variables are interpolated, including dereferencing references. Any block of code can be stuck in place of a reference (it should return a reference, in order to dereference properly). So you can execute any code you want within a regex or a string. The result of the block will be dereferenced and interpolated into the string (here I return a ref to an empty string, so the pattern isn't changed): It will be executed each time the regex is looked at (compiled), even if the match doesn't get that far. For example: `for (qw{dog pig cat horse}) { /.o${print "$_ gets printed\n";\''}/ and print "$_ matched\n"; } __END__ dog gets printed dog matched pig gets printed cat gets printed horse gets printed horse matched` [download] Contrast that with `(?{})`, which executes arbitrary code if the expression matched up to that point (and does not insert anything into your pattern): `for (qw{dog pig cat horse}) { /.o(?{print "$_ gets printed\n"})/ and print "$_ matched\n"; } __END__ dog gets printed dog matched horse gets printed horse matched` [download] And finally `(??{})`, which acts the same, but does insert into your pattern: `for (qw{dog pig cat horse}) { /.o(??{print "$_ gets printed\n"; 'g'})/ and print "$_ matched\n"; } __END__ dog gets printed dog matched horse gets printed` [download] The latter two are "experimental" features, but ref interpolation is not. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re^4: ??{ } oddity by insaniac (Friar) on Apr 28, 2005 at 17:09 UTC
yeah, i needed the insert one ;-) thanks for the explanation of the differences.. to ask a question is a moment of shame to remain ignorant is a lifelong shame	[reply]