Shows how YAML generates back references and JSON does not

gistfile1.rb

2.1.2 :010 >   h = { fruit: 'mango' }
 => {:fruit=>"mango"} 
2.1.2 :011 > a = [h, h]
 => [{:fruit=>"mango"}, {:fruit=>"mango"}] 
2.1.2 :013 > puts a.to_yaml
---
- &1
  :fruit: mango
- *1
 => nil 
2.1.2 :014 > puts JSON::pretty_generate(a)
[
  {
    "fruit": "mango"
  },
  {
    "fruit": "mango"
  }
]