Earlier quoted context omitted.
> variables, like $_. Which you don't use in real programs Oh really? What's wrong with $_ and since when it is?
The problem is that $_ is global and always in package main. A specific problem that fixed this in my memory was a bug in my co-worker's code which boiled down to his looping over an array with $_, then calling a function in his loop that was in a CPAN library that assigned to $_. The result was that he wiped out his whole array. Whenever you are calling out to code that someone else wrote, you don't know if issues l…
It's also lexicalized in every loop, so writing to it doesn't affect anything else. The only time I can think of you would have to worry about this is if some function modified $_ without any loop, and I would consider that a bug (similar to any function that set a static class variable indiscriminately).
For example, the following code performs as expected, and prints "123"
use 5.016;
use warnings;
my @a = qw(1 2 3);
for (@a) {
my @b = qw(4 5 6);
for (@b) {
$_ = 1;
}
print;
}
use 5.016;
use warnings;
sub test {
my @b = qw(4 5 6);
for (@b) {
$_ = 1;
}
}
my @a = qw(1 2 3);
for (@a) {
test;
print;
}
use 5.016;
use warnings;
sub test {
$_ = 1;
}
my @a = qw(1 2 3);
for (@a) {
test;
print;
}