gistfile1.rb

class Foo                                                                        
  def baz                                                                        
    'The original class is noisy'                                                
    raise 'Noise'                                                                
  end                                                                            
end                                                                              
                                                                                 
module MonkeyPatch                                                               
  def self.extended(obj)                                                         
    [ :baz ].each do |meth|                                                      
      obj.define_singleton_method("#{meth}!") do                                 
        obj.class.instance_method(meth).bind(obj).call                           
      end                                                                        
                                                                                 
      instance_eval do                                                           
        define_method meth do                                                    
          begin                                                                  
            send "#{meth}!"                                                      
          rescue => e                                                            
            warn "monkey patch handled #{e} in #{meth}"                          
          end                                                                    
        end                                                                      
      end                                                                        
    end                                                                          
  end                                                                            
end                                                                              
                                                                                 
begin                                                                            
  ff = Foo.new                                                                   
  p ff.baz                                                                       
rescue => e                                                                      
  p "caller handled #{e}"                                                        
end                                                                              
                                                                                 
f = Foo.new                                                                      
f.extend MonkeyPatch                                                             
p f.baz                                                                          
                                                                                 
ff = Foo.new                                                                     
p ff.baz # Oh noez!!