Metaprogramming in Ruby

Just yesterday I started the what I learned today series and I'm already thinking it should have been a weekly digest. Not that I didn't learn anything new (I, in fact, did learn a few things that I will share in a second), I just figured it would be too much noise to publish a digest daily. So weekly it is.

Today I instead want to talk about metaprogramming in Ruby. I actually not so much want to talk about it as I want to put a summary for my future self. Like a collection of links that finally made me get it. The links are in no particular order:

• A great episode of the Ruby Rouges podcast about what metaprogramming is, how it is different from monkey patching, when and why and how you would do it, and beyond. Great stuff. I would actually highly recommend this podcast even to folks not doing Ruby coding on a daily basis (I am not, for example). I have recently picked it up and my commute just got so much better. Haven't yet caught up on all of the episodes.
• Great post from Yehuda Katz about how it's all about self
• This question on SO and the answer to it upvoted 66 times
• Alternatives for redefining methods with pros and cons
• define_method, method_missing, and instance_eval with examples of how Chef DSL is made

I am sure there are more decent blog posts out there on what metaprogramming in Ruby is about and how to do it right and when it is right to do it so please add it to my collection.

UPDATE. As I was wrapping up this one I came across two more very interesting and very relevant posts:

• awesome writeup on include and included. It goes into showing off bizarre examples of massive metaprogramming in ActiveRecord as well as some conscious evolution of rails in doing it more right than it was doing it before
• A response to the post I just mentioned that brings up an interesting point of namespace pollution. While I am ok protecting the global namespace in JavaScript with the "closure everywhere" (function(...){})(); pattern, I am not sure I see the point in giving up syntax convenience and protecting my class namespace in the same way.

What I Learned Today (02/27/12)

There shouldn't be a day in your life when you don't learn something new.

I believe we all learn every day and just not always think about it. I thought I would start a daily digest of things I learned "today" to help me better remember it and to also share it with you as some may find it useful.

Some of it comes from the things I did while working on a problem in the office, some comes from reading or listening to other people, some comes from proof reading my son's homework. There's clearly different depth to the whole notion of "I learned it" so I by no means say that I am now an expert at the things I learned.

Too much "learned" already so with no further due today I have learned:

1. Groovy way of grabbing Maven dependencies via Grape and @Grab import annotations isn't searching in your local .m2 repo. You will need to make an explicit configuration in your .groovy/grapeConfig.xml to make it do a trip "home".
2. Cassandra's secondary index is a hash index so all you can ask it is the equality query. you can't do a range query on it and bitmap secondary indexes are not yet on the roadmap
3. The way you bulk load data into Cassandra is via building SSTable files directly and pushing them to the cluster. Nothing new really, all "databases" do direct datafiles writes for fast bulk inserts but here you literally create datafiles "increments"
4. Ruby has a define operator that you can use to find out if super is defined for the method you're in so you can do things like super if defined?(super). Pretty neat
5. Maven requires you to specify a version of your dependency and would otherwise refuse to build. There's a very popular question on SO why it's this way and how to make it go for the "latest" version.
6. There are 8 planets in our solar systems. There was 9 when I went to school and Pluto was since downgraded to be a dwarf planet with two more dwarfs discovered so it didn't feel lonely