gistfile1.pl

use strict;
use warnings;
use Test::More tests => 4;

do {
    package Class1;
    use Mouse;

    has l => (
        is  => 'ro',
        default => 'A',
    );

    has s => (
        is  => 'ro',
        default => sub { ($_[0]->l || '') . ':B' },
    );

    package Class2;
    use Mouse;

    has s => (
        is  => 'ro',
        default => 'B',
    );

    has l => (
        is  => 'ro',
        default => sub { 'A:' . ($_[0]->s || '') },
    );
};

my $obj1 = Class1->new;
is $obj1->s, ':B';

my $obj2 = Class2->new;
is $obj2->l, 'A:B';


do {
    package Class3;
    use Moose;

    has l => (
        is  => 'ro',
        default => 'A',
    );

    has s => (
        is  => 'ro',
        default => sub { ($_[0]->l || '') . ':B' },
    );

    package Class4;
    use Moose;

    has s => (
        is  => 'ro',
        default => 'B',
    );

    has l => (
        is  => 'ro',
        default => sub { 'A:' . ($_[0]->s || '') },
    );
};

my $obj3 = Class3->new;
is $obj3->s, ':B';

my $obj4 = Class4->new;
is $obj4->l, 'A:B';