When should I use Perl's AUTOLOAD?

Question

In \"Perl Best Practices\" the very first line in the section on AUTOLOAD is:

Don\'t use AUTOLOAD

However all t

Answer 1

I think for a stand alone script this approach is OK. You can create subroutines on the fly to speed up subsequent calls, e.g.:

sub AUTOLOAD {
    (my $name = our $AUTOLOAD) =~ s/.*:://;
    no strict 'refs';  # allow symbolic references

    *$AUTOLOAD = sub { print "$name subroutine called\n" };    
    goto &$AUTOLOAD;   # jump to the new sub
}

Autoloading is tricky when producing inheritance trees.

Answer 2

An alternative strategy would be to write the script as an App::* module and have the commandline option choose which class to load to provide whatever functionality it is that's pluggable depending on the option. You would require that class just-in-time once you know which it is. It's a little more up-front work, but if you intend to maintain the script for a long time, I bet it would pay off. The past couple years have seen the creation of some extra-nice tools for creating scripts whose functionality really lives in modules, including App::Cmd, MooseX::Getopt, and the bastard offspring of both.

Answer 3

If your only reason for using AUTOLOAD is to relocate the block to the end, why not put it at the end in a subroutine, and then call it as soon as its dependent variables are defined?

sub tcpdump;  # declare your subs if you want to call without parens

# define the parameters

compile();

# code that uses new subs

sub compile {
    *tcpdump = $tcpdump ? sub {
        my $msg = shift;
        warn gf_time()." Thread ".threads->tid().": $msg\n";
    } : sub {};
    # ...
}
# EOF

Better still, if the globals aren't needed elsewhere, just pass the values to compile as arguments.