From: Gavin Kistner <gavin.kistner@...>
Date: 2006-10-28T01:39:35+09:00
Subject: Re: nil.to_s != "nil"

From: Eero Saynatkari [mailto:ruby-ml@kittensoft.org] 
> true.to_s  # => "true"
> false.to_s # => "false"
> nil.to_s   # => ""
> 
> "" is not a valid representation of nil. "nil" is.

How do you define "valid"?
obj == eval(obj.to_s)
?

If that is your criteria, then:
a) Most to_s aren't "valid", and
b) #inspect is a better shot

irb(main):001:0> [ true, false, nil, [], "Hello", 1.24 ].each{ |x|
irb(main):002:1* p eval( x.inspect )
irb(main):003:1> }
true
false
nil
[]
"Hello"
1.24