Rails 3 is Ruby 1.9 Only

[ChessMess]

http://www.metabates.com/2010/02/08/ruby-1-9-rails-3-0/

I think it should be 1.9 only as well. It's never fun upgrading but
I'd prefer to do it once then twice.

[Jeremy Kemper]

Rails 3 will definitely prefer Ruby 1.9.2 -- when it’s released -- and
require Ruby 1.8.7 or later.

If you’re running 1.9, I’d recommend building 1.9.2dev rather than
using 1.9.1. It’s big upgrade, it has quite a few behavior changes,
and Rails master is developed against 1.9.2 exclusively (though we do
continuous integration against 1.9.1 for good measure).

The key to *requiring* 1.9.2 is full mysql-ruby, pg, and sqlite3-ruby
encoding support. These database drivers have had ages to upgrade but
still aren’t up to snuff. Pitch in, make it happen, and you’ll find
the database-backed web app world one step behind you.

jeremy