Very similar class to OpenStruct, except all instances are immutable. Use ConstStruct.derive("MyClass") to dynamically create a subclass (so instance.inspect gives a nicer/more specific class name).

conststruct.rb

class ConstStruct
	def self.derive(name)
		cls = Class.new(ConstStruct)
		cls.instance_variable_set :@name, name
		def cls.name;    @name end
		def cls.inspect; @name end
		def cls.to_s;    @name end
		cls
	end

	def initialize(attrs)
		for key, val in attrs
			raise SyntaxError, "illegal method name: #{key}" unless /^[a-z_][a-zA-Z_0-9]*$/ === key

			instance_variable_set :"@#{key}", val
			instance_eval "def #{key}; @#{key} end"

			if TrueClass === val or FalseClass === val
				instance_eval "def #{key}?; @#{key} end"
			end
		end
	end

	def [](name)
		instance_variable_get(:"@#{name}")
	end

	InspectKey = :__inspect_key__ # :nodoc:

	def inspect
		return "<#{self.class}>" if instance_variables.empty?
		str = "<#{self.class} "
		ids = (Thread.current[InspectKey] ||= [])
		if ids.include?(object_id)
			return str << '...>'
		end
	
		ids << object_id
		begin
			str << instance_variables.map {|var|
				"#{var}=#{instance_variable_get(var).inspect}"
			}.join(", ")
			return str << '>'
		ensure
			ids.pop
		end
	end
	alias :to_s :inspect

	def to_hash
		hash = {}
		for var in instance_variables
			svar = var.to_s
			hash[svar.slice(1,svar.length-1).to_sym] = instance_variable_get(var)
		end
		hash
	end
end