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How is metaprogramming in Ruby better?

Joseph Rose

Joined: Feb 02, 2010
Posts: 2

I have recently picked up an interest in Ruby and I am curious to learn about metaprogramming. What makes it different then regular programming practices?

Katrina Owen

Joined: Nov 03, 2006
Posts: 1367
Better? It does seem that asking which is better is a bit like you are comparing raspberries and steak. Both are great, useful, and healthy, but have different (and perhaps complimentary) uses. I don't think I'd want to choose one or the other exclusively.
Paolo Perrotta

Joined: Mar 27, 2010
Posts: 27
It's difficult to explain how metaprogramming works and how it's useful in just a few sentences (unless you already know about it, and then it feels very easy and natural).
Instead, I can point you to the Introduction chapter from Metaprogramming Ruby. You can download it freely here: .

Paolo Perrotta, Europe
Author of Metaprogramming Ruby
David Newton

Joined: Sep 29, 2008
Posts: 12617

Metaprogramming is programming about programming: it's code that writes code, but in a different way than compile-time generation like most Java code generation. Because Ruby is highly dynamic, things like getters and setters can be written by a method that writes additional methods:This ends up generating a class that looks like this:A trivial example, yes, but it's important to understand when and how this is happening. This allows very simple programmatic generation of instance methods *at runtime*. Now think about something like this:Now, with an absolute minimum of intrusiveness, we've defined some instance requirements, at runtime, in code, using a mini-validation DSL. validates_presence_of and validates_length_of are methods that generate behavior.

One thing I worked on was a test framework for web pages. Driving Selenium, I was able to code and test pages like this:

Like Lisp macros, metaprogramming can be difficult to explain, but the power and clarity it can provide is *huge*.
I agree. Here's the link:
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