When you pass an argument to a function, @_ is an alias to these arguments.
So the following works:
use strict;
my $x = 1;
modify_args($x),
print $x, "\n";
sub modify_args {
$_[0] = "modified";
}
__END__
modified
But as soon as you assign the values to a new variable, you create a copy:
my $x = 1;
modify_args($x), # doesn't work
print $x, $/;
sub modify_args {
my ($copy) = @_;
$copy = "modified";
}
__END__
1
Which means that you can change any arguments passed to a sub as long as you stick to manipulating them in @_.
You can circumvent this restriction by passing references , using a module like Data::Bind or Data::Alias), or by creating a new hash and returning that.
If you don't like the last solution (returning a new hash) you should stick to the first one, because of the principle of least surprise: When you call a sub like this: sub_name %hash you don't expect %hash to be modified.
Another possible options are prototypes (notable (\%)), but they come with many problems, and you shouldn't use them until you understood all of these problems |