package Demo;

use Moose;

has test => (is => 'rw', isa => 'ArrayRef');

sub check {
    $self->test(());
}

##</code><code>##

$ perl -c pm_1201774_moose_demo.pm
Global symbol "$self" requires explicit package name (did you forget to declare "my $self"?) at pm_1201774_moose_demo.pm line 8.
pm_1201774_moose_demo.pm had compilation errors.

##</code><code>##

sub check {
    my ($self) = @_;

    $self->test(());
}

##</code><code>##

$ perl -c pm_1201774_moose_demo.pm
pm_1201774_moose_demo.pm syntax OK

##</code><code>##

package Demo;

use Moose;

has test => (is => 'rw', isa => 'ArrayRef');

sub check {
    my ($self) = @_;

    $self->test(());

    $self->test()->[0] = 'X';
}   

package main;

Demo::->new->check;

##</code><code>##

$ perl -c pm_1201774_moose_demo.pm
pm_1201774_moose_demo.pm syntax OK
$ perl pm_1201774_moose_demo.pm
Can't use an undefined value as an ARRAY reference at pm_1201774_moose_demo.pm line 12.

##</code><code>##

$self->test([]);

##</code><code>##

$ perl -c pm_1201774_moose_demo.pm
pm_1201774_moose_demo.pm syntax OK
$ perl pm_1201774_moose_demo.pm
$ 

##</code><code>##

... Fields ... isa => 'HashRef' ...
$self->Fields({});

##</code><code>##

$Cnt = scalar $self->Fields;

##</code><code>##

$ perl -E 'my $x = {a=>1,b=>2}; say scalar $x; say scalar keys %$x'
HASH(0x7ffe120040b0)
2

##</code><code>##

$self->FieldCount = $Cnt;
$self->Changed = -1;

##</code><code>##

... FieldCount ... isa => 'Num' ...
... Changed    ... isa => 'Boolean' ...

##</code><code>##

... Can't modify non-lvalue subroutine call at ...

##</code><code>##

$ perl -E 'my $x = -1; say $x ? "true" : "false"'
true