This was pondered as a Ruby 2.0 feature. Haven't seen wind of any 
concrete ideas yet.

Basically, people can -generally- agree (for given values of every word 
in this sentence) in the longwinded-threads that some form of 
contract-checking wouldn't hurt, but that static typing wouldn't work at 
times. And some alternative forms of contract checking were proposed. 
And many, many flames were exchanged.

David Vallner