From: Gavin Kistner <gavin@...>
Date: 2004-10-22T22:41:27+09:00
Subject: Associating argument descriptions with method

SUMMARY
Why does the code at the end return nil for .arguments?

DETAILS
I'm trying to come up with a system of describing arguments for certain 
public methods, so that my GUI can provide reasonable input widgets and 
constraints. My first idea was to associate this information with each 
method, so that I could discover the public methods and then have each 
method know how to describe itself. However, the following attempt at 
this is leaving me with an empty array.

I'm happy to go another way with this (store the descriptions in an 
instance variable of the class, rather than on each method) but was 
wondering why this doesn't do what I expected.


class UnboundMethod
	attr_accessor :arguments
end

class Method
	class Argument
		attr_accessor :name, :type, :default_value, :required, :min, :max, 
:values

		def initialize( name, type, default_value=nil, required=true, 
min=nil, max=nil, *values )
				@name = name
				@type = type
				@default_value = default_value
				@required = required
				@values = values
		end
	end
end

module MethodDescriptions
	@@describe_method = lambda { |id, name, help, return_type, *arguments|
		self.instance_method( id ).arguments = arguments
	}

	def self.extend_object( obj )		
		obj.send( :define_method, :describe_method, @@describe_method )
	end
end

class Foo
	self.extend( MethodDescriptions )

	def calculate_area( length, width )
		length * width
	end
	
	nil && describe_method( :calculate_area, 'Calculate Area',
		'Calculates the area of a rectangle',
		Method::Argument.new( :return, :float ),
		Method::Argument.new( :length, :float, 0, true, 0 ),
		Method::Argument.new( :width, :float, 0, true, 0 )
	)
end

m = Foo.instance_method( :calculate_area )
p m, m.arguments

#=> #<UnboundMethod: Foo#calculate_area>
#=> nil
--
(-, /\ \/ / /\/