オーバーロードっぽいことをする

overload.rb

# -*- coding: utf-8 -*-
def Object.defun(symbol, *signature, &blk)
  instance_variable_set(:@overloaded_methods, {}) if @overloaded_methods.nil?
  klass = self
  unless @overloaded_methods.key? symbol
    @overloaded_methods[symbol] = {}
    # super()を使ったり、実際のメソッドと同じ挙動にするにはdefine_methodを使うしかないので
    overload = Proc.new { |*args|
      oms = klass.instance_variable_get(:@overloaded_methods)
      sig = Signature.new(*args)
      if oms[symbol].key?(sig)
        klass.method(:define_method).call(symbol, oms[symbol][sig])
        ret = method(symbol).call(*args)
        klass.method(:define_method).call(symbol, overload)
      end
      ret
    }
    define_method(symbol, overload)
  end
  @overloaded_methods[symbol][Signature.new(*signature)] = blk
end
class Signature
  def initialize(*signature)
    @signature = signature.map { |klass|
      klass.is_a?(Class) ? klass : klass.class
    }
  end
  def [](index); @signature[index]; end
  def hash; @signature.hash; end
  def ==(obj); @signature == obj.instance_variable_get(:@signature); end
  def eql?(obj); @signature == obj.instance_variable_get(:@signature); end
  def to_s; "(#{@signature.join(', ')})"; end
end

class A
  defun(:homu, String) { |str| puts "I'm homu(String)" }
  defun(:homu, Array) { |array| puts "I'm homu(Array)" }
end

class B < A
  defun(:homu, String) { |str| super(str) }
end
A.new.homu("")
A.new.homu([])
B.new.homu("")