Ruby's widely admired simplicity has a downside: too many Ruby and Rails applications have been created without concern for their long-term maintenance or evolution. The Web is awash in Ruby code that is now virtually impossible to change or extend. This text helps you solve that problem by using powerful real-world object-oriented design techniques, thoroughly explained via simple and practical Ruby examples. Sandi Metz has distilled a lifetime of conversations and presentations about object-oriented design into a proven set of Ruby-focused practices for crafting manageable, extensible, and pleasing code. She demonstrates how to build new applications that can survive success, and repair existing applications that have become impossible to change. Each technique is illustrated with extended examples, all downloadable from the companion Web site, poodr.info. Fully updated for Ruby 2.X, this guide shows how to:Decide what belongs in a single Ruby class Avoid entangling objects that should be kept separate Define flexible interfaces among objects Reduce programming overhead costs with duck typing Successfully apply inheritance Build objects via composition Design cost-effective tests Solve common problems associated with poorly designed Ruby code Whatever your previous Ruby experience, Practical Object-Oriented Design in Ruby, Second Edition will guide you to the superior outcomes you're looking for.