use Perl

I just blew a nice chunk of time debugging the following problem:

use constant DEFAULT_ARGS => [qw/some data/];

...

unless (@_) {
    $self->{args} = DEFAULT_ARGS;
}

Later on in my code, I had this:

my $args = $self->args;
while ( defined (my $curr_arg = shift @$args) ) {
    # do something while blithely ignoring
    # the havoc we're wreaking
}

See the bug? The two accidentally coupled lines of code were 214 lines apart and appeared to be unrelated. That was a bugger to track down. The fix I used was to simple clone those args when needed, but my longer-term fix is to not use constants. Use ReadOnly:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper::Simple;
use ReadOnly;

use constant FOO => [qw/bar baz/];
my $data = FOO;
shift @$data;
print Dumper(FOO);

Readonly::Scalar my $foo => [qw/bar baz/];
$data = $foo;
shift @$data;
print Dumper($foo);

And the output:

$FOO = [
  'baz'
];
Modification of a read-only value attempted at constant.pl line 15