• method_missing，顾名思义，在方法找不到时被调用。有了这个强大元编程工具，我们就能创建动态的方法，比如ActiveRecord中的动态finder

class Legislator
  # Pretend this is a real implementation
  def find(conditions = {})
  end

  # Define on self, since it's  a class method
  def self.method_missing(method_sym, *arguments, &block)
    # the first argument is a Symbol, so you need to_s it if you want to pattern match
    if method_sym.to_s =~ /^find_by_(.*)$/
      find($1.to_sym => arguments.first)
    else
      super
    end
  end
end

• send，也是一个动态方法调用的强大工具，它的作用的将一个方法以参数的形式传递给对象。 ``` class Box def open_1 puts “open box” end

  def open_2 puts “open lock and open box” end

  def open_3 puts “It’s a open box” end

  def open_4 puts “I can’t open box” end

  def open_5 puts “Oh shit box!” end end

box = Box.new

box.send(“open_#{num}”) ```