Rubyのメタプログラミングを極める：コードを自在に操る技術

class DynamicMethods
  def method_missing(name, *args)
    puts "Method #{name} called with arguments: #{args}"
  end
end
obj = DynamicMethods.new
obj.hello("world")

class DynamicClass
  [:foo, :bar].each do |method_name|
    define_method(method_name) do
      puts "#{method_name} method called"
    end
  end
end
obj = DynamicClass.new
obj.foo
obj.bar

class MyClass
end
MyClass.class_eval do
  def greet
    "Hello!"
  end
end
puts MyClass.new.greet

obj = "Hello"
def obj.shout
  upcase
end
puts obj.shout

module Greetable
  def greet
    "Hello, #{name}!"
  end
end
class User
  attr_accessor :name
end
user = User.new
user.name = "Alice"
user.extend(Greetable)
puts user.greet

class MonitorMethods
  def self.method_added(name)
    puts "Method #{name} was added"
  end

  def new_method
    # dummy method
  end
end

class Proxy
  def initialize(target)
    @target = target
  end

  def method_missing(name, *args, &block)
    puts "Calling #{name} on target"
    @target.send(name, *args, &block)
  end
end
proxy = Proxy.new([1, 2, 3])
proxy.push(4)