Developing Thoughts

While trying to figure out how to get MysqlAdapter to do something, it occurred to me one big difference between Ruby (which I’m relatively new to) and Lisp (which I’ve played with for years).

Where Lispers use hooks, Rubyists use monkeypatching.

It’s not a technical difference, because you can monkeypatch in Lisp and you can use hooks in Ruby. Maybe it’s a question of maturity: programmers don’t want to add hooks that won’t get used, and so only add them lazily.  It certainly seems true that older Lisp code is more likely to have more hooks: Common Lisp itself has a million hooks, and Emacs, says the jargon file, “is all hooks”.  Maybe it’s natural selection: Lisp libraries either end up with lots of hooks, or dead.

The Ruby way has advantages and disadvantages.  On the plus side, a young project doesn’t have to guess what people might want to extend.  On the downside, well, it’s monkey-patching.

(For example, the problem that inspired this post led me to monkey-patching a private method.  It looks like you can monkey-patch a private method, but you can’t call ’super’ in it, because super is private. Gah.  And ActiveRecord has basically no hooks.)

Even Zed Shaw, flamester extraordinaire, hates it.  Monkey-patching is ghetto.

What I really want is a hybrid Lisp/Ruby solution: CLOS qualifiers in Ruby.  A qualifier is a keyword you pass to defmethod — :before or :after or :around — which causes it to supplement, rather than replace, the (unqualified) method definition that already exists. It’s like hooks everywhere for free.

That is, I want to be able to say:

class MysqlAdapter
  def :after connect
    execute("SET SESSION sql_mode='ANSI'")
  end
end

(Now somebody is going to write me some super-twisted Ruby code to allow exactly that, and it’s going to be like monkey-patching but 10 times worse because it’ll be implemented as one giant monkey-patch.  Thanks, no.)

But in plain old Ruby, what’s the solution?  If you write a library, it needs hooks — especially if you’re part of a big framework, like ActiveRecord is.  And if you design a programming language, it should make allowing hooks virtually free for people writing libraries.