redefining a single ruby method on a single instance with a lambda

Question

In Ruby, is there a way to redefine a method of a particular instance of a class using a proc? For example:

class Foo
  def bar()
    return \"hello\"
  end         


        

Answer 1

I'm not sure what version of Ruby this was added in (at least 1.8.7), but there seems to be an even simpler way of doing this:

str1 = "Hello"
str2 = "Goodbye"
def str1.to_spanish
  "Hola"
end
puts str1 # => Hello
puts str1.to_spanish # => Hola
puts str2 # => Goodbye
puts str2.to_spanish # => Throws a NoMethodError

Learnt about this whilst reading the Ruby Koans (about_class_methods.rb lesson). I'm still not entirely sure what the purpose of this is since it seems a bit dangerous to me.