Ruby Metaprogramming Episode 7: More Hook Methods

We’ll pick up where we left off in the last episode by looking at two more Ruby hook methods: included and method_added. But we’ll also take it a step further. We’ll use these hook methods to develop a metaprogramming library that traces the execution of a Ruby program. Along the way we’ll see all the various subtle (and important!) things you need to think about when you’re trying to write a general-purpose metaprogramming library.

• Using included to intercept when a module is included in a class, and use it to set up another hook method in a different context
• Using method_added to track when a new method is defined on a class, and trace the method’s execution
• Refactoring the tracing to support blocks
• Using method objects to bypass naming issues
• Adding tracing to methods that have already been added
• Suppressing tracing for certain methods
• Using Thread.current to define thread-local variables
• Differences between Ruby 1.8 and 1.9
• Practical examples (and corner cases) of metaprogramming