use strict;
use warnings;
package Foo;
sub new {
    my ($class, $arg) = @_;
    my $this = bless {}, $class;
    $this->{args} = undef;
    return $this;
}
sub set {
    my ($this, $arg) = @_;
    $this->{args}[0] = $arg; # setting an entry in a shared array reference
}
1;
# End of the module, and now a test script
use strict;
use warnings;
use Foo;
use threads;
use threads::shared;

my $foo = new Foo();
my $nested_array = [];
my $nested_string = 'bar';

share($foo);
share($nested_array);
share($nested_string);

$foo->{args} = $nested_array; # set the shared array reference
# pass in a reference to the shared scalar
my $thr1 = threads->create(sub { $foo->set(\$nested_string) });
<Update>
# If in Foo::set we manually set the argument passed, say, to 'quux', 
# the object will contain that string rather than 'bar',
# proof that we do indeed have a shared nested reference.
</Update>
$thr1->join();
print $foo->{args}[0];