rails/rails — pull request #8142 by nikitug (2012-11-08 09:19:08+00:00)
Title: Implement `Hash#deep_diff`, the recursive difference between two hashes.

Here is an example:

```ruby
{ a: { b: 1 }}.deep_diff(a: { b: 1 }) # => {}
{ a: { b: 1, c: 2 } }.deep_diff(a: { b: 1 }) # => { a: { c: 2 } }
{ a: { b: 1 } }.deep_diff(a: { b: 1, c: 2 }) # => { a: { c: 2 } }
```