Ruby errors

ruby_errors.rb

# Ruby-doc documentation from http://ruby-doc.org/core-2.0/Object.html#method-i-class
guy = "Bob"
guy.define_singleton_method(:hello) { "#{self}: Hello there!" }
guy.hello    #=>  "Bob: Hello there!"

# ------------------------------------------------------------------------------

# Here is what I get on my machine:

guy = "Bob"
# ==> "Bob"
guy.define_singleton_method(:hello) { "#{self}: Hello there!" }
# =NoMethodError: undefined method `define_singleton_method' for "Bob":String
# = from (irb):71
guy.hello
# =NoMethodError: undefined method `hello' for "Bob":String
# = from (irb):72