如何檢查是否一個Ruby的功能（不是方法）存在

Question

在Sinatra寶石有production?和development?功能， 如何檢查腳本是有史以來需要Sinatra 或者有production?和development?函數曾經定義？

可能是更好的解釋：

script1.rb: 
# there is possibility that this script contains "require 'sinatra'" 
# note that sinatra defines 'production?' and 'development?' function 

script2.rb: 
# there is possibility that this script already has defining 'production?' function 

script3.rb: 
require_relative 'script1' 
require_relative 'script2' 
... 
require_relative 'scriptX' 
# in this script, how to know if there are at least one script that has already defining 'production?' function? 

Answer 1

啊哈！使用defined?

require 'ap' 

ap defined? production? 
# nil 

def production? 
end 

ap defined? production? 
# 'method'