From: Sam Smoot <ssmoot@...>
Date: 2007-06-16T07:30:06+09:00
Subject: Get Parameter names from methods

Oft asked for, here you go:

> module Kernel
>
>   PARAMETERIZED_CLASSES = {}
>
>   def parameterized_require(libpath)
>     libpath = libpath + '.rb' unless libpath =~ /\.rb$/
>
>     load_path = $LOAD_PATH.find do |search_path|
>       File.exists?(File.join(search_path, libpath))
>     end
>
>     if load_path.nil? && !File.exists?(libpath)
>       raise LoadError.new("Could not find library path: #{libpath}")
>     end
>
>     file_path = (load_path.nil? ? libpath : File.join(load_path, libpath))
>     contents = File.read(file_path)
>
>     contents.scan(/^\s*class\s(\w+)/) do |class_name|
>       PARAMETERIZED_CLASSES[class_name.first.freeze] = file_path
>     end
>
>     require(libpath)
>
>   rescue => e
>     raise LoadError.new(e)
>   end
>
> end
>
> class UnboundMethod
>
>   def binding_class
>     @class_name || @class_name = begin
>       to_s =~ /\#\<UnboundMethod\:\s(\w+)/
>       Object.const_get($1)
>     end
>   end
>
>   def name
>     @name || @name = begin
>       to_s =~ /\#\<UnboundMethod\:\s\w+\#(\w+)/
>       $1.freeze
>     end
>   end
>
>   def parameters
>     @parameters || @parameters = begin
>       parameter_names = []
>
>       if file_path = PARAMETERIZED_CLASSES[binding_class.name]
>         if match = /def\s+#{name}\!?(\s+(.+)|\((.+)\))(\;|$)/.match(File.read(file_path))
>           parameters_capture = match.captures[1] || match.captures[2]
>           parameter_names = parameters_capture.split(/\,\s*/).reject do |parameter_name|
>             parameter_name.empty? || parameter_name == 'nil'
>           end.map { |s| s.freeze }
>         end
>       end
>
>       parameter_names
>     end
>   end
>
> end

There's holes in this. It's not a full Ruby parser. But it should work
for 99% of your files.

The idea is to extend web MVC frameworks like Merb to allow actions
like the following:

> class Post
>   def show(id)
>     @post = Post.find(id)
>   end
> end

I got the idea from a .NET project based _loosely_ on Rails:
http://castleproject.org/monorail/index.html

The problem is Ruby doesn't provide reflection similar to c#'s
ParameterInfo object to make this easy. So here we are. I hope someone
else finds this useful.