ref nested_a: HASH
ref nested_b: MCE::Shared::Object
ref nested_c: MCE::Shared::Object
ref nested_d: MCE::Shared::Object

a: $VAR1 = bless( {
                 'key' => 2,
                 'nested' => {
                               'key' => 1
                             }
               }, 'MCE::Shared::Hash' );

b: $VAR1 = bless( {
                 'key' => 2,
                 'nested' => bless( {
                                      'key' => 3
                                    }, 'MCE::Shared::Hash' )
               }, 'MCE::Shared::Hash' );

c: $VAR1 = bless( {
                 'key' => 2,
                 'nested' => bless( {
                                      'key' => 3
                                    }, 'MCE::Shared::Hash' )
               }, 'MCE::Shared::Hash' );

d: $VAR1 = bless( {
                 'key' => 2,
                 'nested' => bless( {
                                      'key' => 3
                                    }, 'MCE::Shared::Hash' )
               }, 'MCE::Shared::Hash' );