dynamic_method.rb

# =====================
# Spell: Dynamic Method
# =====================

# Decide how to define a method at runtime.

class C
end

C.class_eval do
  define_method :my_method do
    "a dynamic method"
  end
end

obj = C.new
obj.my_method # => "a dynamic method"

# For more information: http://www.pragprog.com/titles/ppmetr/metaprogramming-ruby