sub upack_with_shift {
    my $foo = shift;
    my $bar = shift;
    my $baz = shift;
    
    .... DO STUFF ...
}

sub list_assignment {
    my ( $foo, $bar, $baz ) = @_;
}

sub direct_access {
    $_[0] = "PROCESSED";
    $_[1] += $_[2];
    $_[2] = undef;

    return 1;
}

# direct access is dangerous.  Perl passes sub arguments by reference.
# it is possible to change values in a calling function's variables if you aren't careful.
my use_da {
    my @foo = ('', 5, 7);

    my $result = direct_access( @foo );   
    print join ', ', $result, @foo;
    # prints: 1, PROCESSED, 
    # generates a warning if warnings on.  "Use of uninitialized value in join at line mumble" 

}