Re^2: shift vs @_

[BerntB]

Assume I have some large strings. I don't want them copied when I send them as parameters to subroutines/methods (which doesn't modify them).

Do I have to use the $_[x] notation for that? Should I send them in as references?

[shmem]

Both ways are ok. $_[0] is actually a reference (thanks, tye!) an alias to the first argument passed by the caller. You can evaluate (or operate on) $_[0] directly. Passing arguments as references just adds another level of indirection.

You can also use prototypes for your subs and access your arguments inside the sub as references:

#!/usr/bin/perl
sub foo(\@\$) {
    warn "foo args: (".join(",",map{"'$_'"}@_).")\n";
    print "1st argument = $_[0]; content =("
         . join(',',map{"'$_'"} @{$_[0]}).")\n";
    print "2nd argument = $_[1]; content = '".${$_[1]}."'\n";
    my ($array,$scalar) = @_;
    push @$array, $$scalar;
    $$scalar = "blurf";
} 
my @ary = qw(foo bar baz);
my $foo = "blah";

foo(@ary,$foo);

print "ary: (@ary)\n";
print "foo: $foo\n";

output:

foo args: ('ARRAY(0x8167870)','SCALAR(0x8167978)')
1st argument = ARRAY(0x8167870); content =('foo','bar','baz')
2nd argument = SCALAR(0x8167978); content = 'blah'
ary: (foo bar baz blah)
foo: blurf

--shmem

[tye]

$_[0] is actually a reference to the first argument passed by the caller.

I'm sure you know what you meant, but... $_[0] is (usually) an alias to the first argument. If it were a reference then you'd have to use ${$_[0]} or such.