Ruby Multi-dispatch

multi-dispatch.rb

module Kernel
  MDEF_DEFINED = {}

  def mdef(name, *types, &block)
    sig = gen_sig(name, types)
    MDEF_DEFINED[name] = (MDEF_DEFINED[name] || []) + [ sig ]
    Kernel.send(:define_method, sig, &block)
  end

  def gen_sig(name, types)
    [ name, types.map(&:to_s).join("_") ].compact.join("_")
  end

  def method_missing(name, *args)
    if defs = MDEF_DEFINED[name]
      sig = gen_sig(name, args.map { |a| a.class })
      return send(sig, *args) if defs.include?(sig)
    end

    super(name, *args)
  end
end
















mdef(:met, Fixnum) do |arg|
  arg + arg
end

mdef(:met, String) do |str|
  str.upcase
end

puts met(1)    # 1 + 1 = 2
puts met("a")  # a -> A