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# # How to use alias to redefine or mock a class method. # # This example will show how to redefine a class method, # then restore the method back to it's original behavior. # # by Greg Houston # blog: http://ghouston.blogspot.com/ # # Also of note, the gem Mocha uses the same technique to mock class methods. # We will need access to the meta class. module Kernel # singleton_class => singleton class of receiver # # source: http://ola-bini.blogspot.com/2006/09/ruby-metaprogramming-techniques.html # source: RCR231 # unless Kernel.respond_to? :singleton_class def singleton_class class << self; self; end end end end # the Brain is our lab rat for this example class Brain def Brain.who "I am the Brain" end end # first, alias the method we will redefine... Brain.singleton_class.class_eval do alias :backup :who end Brain.who #=> I am the Brain Brain.backup #=> I am the Brain # second, redefine the method Brain.singleton_class.send :define_method, :who do "Actually I am a genetically altered lab mouse bent on world domination!" end Brain.who #=> Actually I am a genetically altered lab mouse bent on world domination! Brain.backup #=> I am the Brain # third, restore the original definition, and remove the backup... Brain.singleton_class.class_eval do alias :who :backup undef :backup end Brain.who #=> I am the Brain Brain.backup #=> undefined method `backup' for Brain:Class (NoMethodError)

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