problem in active_support/string/access.rb?

There is this:

          def first(limit = 1)
            chars[0..(limit - 1)].to_s
          end

but in console when I try it I get:

"test".first

NoMethodError: undefined method `[]' for #<Enumerable::Enumerator:
0x2242b90>
  from /usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/
active_support/core_ext/string/access.rb:43:in `first'
  from (irb):1

because it is doing "test".chars[0..0]

Or am I missing something here?