Question

I have a class with some methods. It’s supersekret but I’ve reproduced what I can here.

Class RayGun   # flashes red light   # requires confirmation   # makes 'zowowowowowow' sound   def stun!     # ...   end    # flashes blue light   # does not require confirmation   # makes 'trrrtrtrtrrtrtrtrtrtrtr' sound   def freeze!     # ...   end    # doesn't flash any lights   # does not require confirmation   # makes Windows startup sound   def killoblast!     # ...   end end 

I want to be able to, at runtime, interrogate the class about one of the methods and receive a hash or struct like so:

  {:lights => 'red', :confirmation => false, :sound => 'windows'} 

What’s the best way of doing this? Obviously you could have separate YAML file alongside and set up a convention to relate the two, but ideally I want code and metadata in one place.

The most promising idea I can come up with is something like this:

class RayGun   cattr_accessor :metadata   def self.register_method(hsh)     define_method(hsh.name, hsh.block)     metadata[hsh[:name]] = hsh   end    register_method({     :name => 'stun!',      :lights => 'red',      :confirmation => 'true',      :sound => 'zowowo',     :block => Proc.new do       # code goes here    })     # etc. end 

Anyone got some better ideas? Am I barking up a very wrong tree?

Answer 1

I found another strategy poking around http://github.com/wycats/thor/tree. Thor lets you write stuff like this:

Class RayGun < Thor   desc 'Flashes red light and makes zowowowowow sound'   method_options :confirmation => :required   def stun!     # ...   end end 

It manages this by using the (undocumented) hook Module#method_added. It works like this:

1. Call to Thor#desc and Thor#method_options set instance variables @desc, @method_options.

2. Defining method stun! calls Thor#method_added(meth)

3. Thor#method_added registers Task.new(meth.to_s, @desc, @method_options) (roughly speaking) and unsets @desc, @method_options.

4. It’s now ready for the next method

Neat! So neat that I am going to accept my own answer 🙂