Objective-C-esque calling convention in Ruby (or: Why I shouldn't be let near method_missing)

objc_calling.rb

# See the bottom of the file for how this actually works.

module ObjC
  def method_missing(method, *args)
    ObjCCall.new(self, [], []).send(method, *args)
  end
end

class ObjCCall
  def initialize(obj, selector, args)
    @obj = obj
    @selector = selector
    @args = args
  end

  def method_missing(method_sym, *args)
    # This is for a more authentic Objective C experience.
    #if @args.length > @selector.length
    #  raise ArgumentError, "You can only specify multiple arguments if it's the end of the method."
    #end

    method = method_sym.to_s
    should_call = false
    if method.end_with?('!')
      method = method[0...-1]
      should_call = true
    end

    ret = self.class.new(@obj, @selector + [method], @args + args)
    ret = ret._send_call if should_call

    ret
  end

  def _selector
    @selector.join('_').to_sym
  end

  def _valid_call
    @obj.respond_to?(_selector)
  end

  def +@; _send_call; end
  def _send_call
    if _valid_call
      @obj.send(_selector, *@args)
    else
      raise NoMethodError, "undefined method `#{_selector}' for #{@obj.inspect}:#{@obj.class}"
    end
  end
end


if $0 == __FILE__
  class Test
    include ObjC

    def do_thing_with_other_thing(thing1, thing2)
      [thing1, thing2]
    end
  end


  test = Test.new

  puts "ObjC Call!"
  puts (+test.do_thing('laugh').with_other_thing('face')).inspect
  puts

  puts "Alternate ObjC Call!"
  puts test.do_thing('laugh').with_other_thing!('face').inspect
end

objc_calling_magic.rb

# See the bottom of the file for how this actually works.

require 'objc_calling'

module ObjCMagic
  def method_missing(m, *args)
    ObjCCallMagic.new(self, [], []).send(m, *args)
  end
end

class ObjCCallMagic < ObjCCall
  def method_missing(m, *args)
    ret = super
    if ret.kind_of?(ObjCCall) and @obj.respond_to?(ret._selector)
      ret._send_call
    else
      ret
    end
  end
end


if $0 == __FILE__
  class TestMagic
    include ObjCMagic

    def some_thing_with_other_thing(thing1, thing2)
      [thing1, thing2]
    end
  end

  puts "ObjC Call, Magic Edition!"
  puts TestMagic.new.some_thing(1).with_other_thing(2).inspect
end

This is why we can't have nice things!