So I would say that any code that *sets* $_ is, by definition, wrong.
Unnecessary, perhaps, but not wrong. Setting $_ can be useful:
- As a topicalizer in a single-item for loop, to make a series of operations on a common value read more cleanly.
Instead of this:
$h->{foo}{bar} =~ s/[._]/ /g;
Some::Custom::Function($h->{foo}{bar});
$h->{foo}{bar} =~ s/^\s+//;
$h->{foo}{bar} =~ s/\s+$//;
$h->{foo}{bar} =~ s/`/'/g;
You can write this:
for ($h->{foo}{bar}) {
s/[._]/ /g;
Some::Custom::Function($_);
s/^\s+//;
s/\s+$//;
s/`/'/g;
};
-
And the occasional weird circumstance, like conveniently modifying the values of a hash:
map { $_ = foo( $bar, $_ ) } values %somehash;
On the other hand, where
real for loops are concerned, I find it reduces confusion to always provide your own lexical topic (e.g.
for my $key (@keys) { ... } ). A bit backwards from the way the language is designed, I suppose.