What happens when you run class_eval on something that's not a class?

Question

test = "a" test.class_eval do # what is going on here??? end

Answer 1

Well, on my computer, you get a NoMethodError because the String class doesn't have a class_eval method :)

Answer 2

I think that in vanilla Ruby, that is illegal. For instance, if you try it in irb, you'll get a NoMethodError.

In a rails console, there might be extra methods added in that cause strings to behave like classes.

Answer 3

ActiveSupport adds class_eval to Object so it can be used on anything, not just classes.

In your example, what it does is the equivalent of:

test = "a"
class << test
  # do stuff
end

The actual implementation as of Rails 2.3 is here: http://github.com/rails/rails/blob/2-3-stable/activesupport/lib/active_support/core_ext/object/singleton_class.rb