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Changing a class later on - Ruby

In Ruby, you can define a class ... and then come back and add methods to it. But why would you want to?

Let's suppose that you've got a base class - I'll use "Rectangle" as my example, and you've already subclassed it to "Square" and perhaps a few other things, via a required file that you share between a number of programs. Then you want to use that group of classes in a new application, but with a modification to one of the base methods. The example I used during yesterday's course was that the rectangles were pictures, and I wanted to add a frame, 1 unit wide, around them in my new code. [full source].

Well - given that scenario, you've got an excellent excuse for going back within your own code and replacing the methods of Rectangle that are changed when you add a frame, and it'll be the new routines that are run when you call methods in the already-defined subclasses. It's very neat indeed, and the alternative would be ugly.

(written 2011-02-02)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
R108 - Ruby - More Classes and Objects
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  [4550] Build up classes into applications sharing data types in Ruby - (2015-10-23)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [3782] Standard methods available on all objects in Ruby - (2012-06-23)
  [3781] Private, Protected, Public in Ruby. What about interfaces and abstract classes in Ruby? - (2012-06-23)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3158] Ruby training - some fresh examples for string handling applications - (2011-02-05)
  [3142] Private and Public - and things between - (2011-01-22)
  [2980] Ruby - examples of regular expressions, inheritance and polymorphism - (2010-10-02)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2623] Object Oriented Ruby - new examples - (2010-02-03)
  [2620] Direct access to object variable (attributes) in Ruby - (2010-02-02)
  [2616] Defining a static method - Java, Python and Ruby - (2010-02-01)
  [2604] Tips for writing a test program (Ruby / Python / Java) - (2010-01-29)
  [2603] Ruby objects - a primer - (2010-01-29)
  [2601] Ruby - is_a? v instance_of? - what is the difference? - (2010-01-27)
  [2292] Object Orientation in Ruby - intermediate examples - (2009-07-16)
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [184] MTBF of coffee machines - (2005-01-20)


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