package Wibble;
use Moose;

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

package main;

my $w = Wibble->new( thingies => [ 'this', 'that' ] );
print join( ", ", @{ $w->thingies() } ) . "\n";
$w->thingies('another');
print join( ", ", @{ $w->thingies() } ) . "\n";

__END__
this, that
Attribute (thingies) does not pass the type constraint because: Validation failed for 'ArrayRef' failed with value another at (eval 69) line 7
	Wibble::thingies('Wibble=HASH(0x1274b38)', 'another') called at 742018.pl line 10