Metaprogramming Ruby 2

The Fall of alias_method_chain

In the previous two chapters, you’ve seen that the libraries in Rails are mostly built by assembling modules. Back in Rails 2, many of those modules used alias_method_chain to wrap functionality around the methods of their includers. The authors of libraries that extended Rails adopted the same mechanism to wrap their own functionality around the Rails methods. As a result, alias_method_chain was used all over the place, both in Rails and in dozens of third-party libraries.

alias_method_chain was good at removing duplicated aliases, but it also came with a few problems of its own. For a start, alias_method_chain is just an encapsulation of an Around Alias (Around Alias), and Around Aliases have the subtle problems ...