Re^5: Missing $ on loop variable

As for the "obsolete" part, i used it --evidently badly-- as a synonym to "since there is no other code ... in the foreach block". Of course i was only refering to this snippet since next is invaluable in loop control. But i'm sure you knew that already. ;)

As for the grep gotcha, here is the situation. Given this code:

my $line = "Alpha and some beta junk here";
my @keywords = qw(alpha beta gamma);

foreach (grep { $line =~ /$_/i } @keywords) {
    $_ = rand;
}

foreach (@keywords) { print "$_\n" }
[download]

We get when run:

0.623870849609375
0.16607666015625
gamma
[download]

Grep aliases the current value of $_ to the original array element, and thus modifying it actually tampers our original data. It wasn't any special complication really, but has the potential to obfuscate a bug or two.

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Re^6: Missing $ on loop variable by revdiablo (Prior) on Dec 03, 2005 at 19:27 UTC
Grep aliases the current value of $_ to the original array element, and thus modifying it actually tampers our original data That's true, and good to point out. But it's also good to point out that `for` does the same thing. And the solution with grep is the same -- copy the values before modifying them. Which, incidentally, is exactly what my example snippet does. It copies the values into a new array. If you plug my example in just as I wrote it, the problem goes away: `my $line = "Alpha and some beta junk here"; my @keywords = qw(alpha beta gamma); my @found = grep { $line =~ /$_/i } @keywords; foreach (@found) { $_ = rand; } print "@keywords\n"; __OUTPUT__ alpha beta gamma` [download] So, while the gotcha didn't affect my example directly, I'm glad you brought it up. Anyone who wasn't aware of it will likely benefit from this discussion.	[reply] [d/l] [select]

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Re^6: Missing $ on loop variable
by revdiablo (Prior) on Dec 03, 2005 at 19:27 UTC

Grep aliases the current value of $_ to the original array element, and thus modifying it actually tampers our original data

That's true, and good to point out. But it's also good to point out that for does the same thing. And the solution with grep is the same -- copy the values before modifying them. Which, incidentally, is exactly what my example snippet does. It copies the values into a new array. If you plug my example in just as I wrote it, the problem goes away:

my $line = "Alpha and some beta junk here";
my @keywords = qw(alpha beta gamma);

my @found = grep { $line =~ /$_/i } @keywords;

foreach (@found) {
    $_ = rand;
}

print "@keywords\n";

__OUTPUT__
alpha beta gamma
[download]

So, while the gotcha didn't affect my example directly, I'm glad you brought it up. Anyone who wasn't aware of it will likely benefit from this discussion.

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