“响应？”与“响应缺失？”

定义的意义何在respond_to_missing?而不是定义respond_to?？如果重新定义会出现什么问题respond_to?某堂课？

Without respond_to_missing? http://ruby-doc.org/core/Object.html#method-i-respond_to_missing-3F已定义，尝试通过获取该方法method http://ruby-doc.org/core/Object.html#method-i-method将失败：

class Foo
  def method_missing name, *args
    p args
  end

  def respond_to? name, include_private = false
    true
  end
end

f = Foo.new
f.bar  #=> []
f.respond_to? :bar  #=> true
f.method :bar  # NameError: undefined method `bar' for class `Foo'

class Foo
  def respond_to? *args; super; end  # “Reverting” previous redefinition

  def respond_to_missing? *args
    true
  end
end

f.method :bar  #=> #<Method: Foo#bar>

马克-安德烈 https://stackoverflow.com/users/8279/marc-andre-lafortune（Ruby 核心提交者）有一个很好的博客文章于respond_to_missing? http://blog.marc-andre.ca/2010/11/methodmissing-politely.html.