The implict reference is not a hard reference, as perlref speaks of, but an aliasing that occurs. For example:
sub x {
$_[0] = "in x";
}
my $foo = "outside";
x($foo);
... will set
$foo to "in x". The thing in
@_ has become an alias for
$foo. However, you won't get this behavior if you explictly copy the value out of
@_, as in:
sub x {
my($foo) = @_;
$foo = "in x";
}
my $foo = "outside";
x($foo);
When you copy the value, you are not working with an alias to the thing passed in, but you a working with a copy, bringing you the pass-by-value semantics that are probably more intutitive to you.