kernel#require_relative
Ruby tries to load the library named string relative to the requiring file's path. 就是说当前运行文件的目录下面找这个要加载的文件。
如：/Users/个人/Ruby元编程/object_model/hook.rb:
#require(name) -> true/false
用于加载标准库，就是和Ruby一起安装的库。
from /Users/个人/.rvm/rubies/ruby-2.5.0/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
https://stackoverflow.com/questions/4467538/what-does-the-operator-do-in-ruby
关于 === operator的用法。是一个包含运算符号：
a === b :a是否包含b，是的话返回true，不是返回false.
t's a boolean operator which asks the question "If I have a drawer labelleda would it make sense to put b in that drawer?"