> w = nil
> x = "foo" if w != nil # still assigns foo to x

It doesn't for me:

irb(main):001:0> w = nil
nil
irb(main):002:0> x = 'foo' if w != nil
nil
irb(main):003:0> x
nil
irb(main):004:0> VERSION
"1.6.6"

Chris   
http://clabs.org