# bad
  arr = Array.new
  hash = Hash.new

  # good
  arr = []
  hash = {}

  # bad
  STATES = ['draft', 'open', 'closed']

  # good
  STATES = %w(draft open closed)

  # bad
  STATES = [:draft, :open, :closed]

  # good
  STATES = %i(draft open closed)

  # bad - easier to move/add/remove items, but still not preferred
  VALUES = [
        1001,
        2020,
        3333,
       ]

  # bad
  VALUES = [1001, 2020, 3333, ]

  # good
  VALUES = [1001, 2020, 3333]

  arr = []
  arr[100] = 1 # now you have an array with lots of nils

  # bad
  hash = { 'one' => 1, 'two' => 2, 'three' => 3 }

  # good
  hash = { one: 1, two: 2, three: 3 }

  # bad
  hash = { :one => 1, :two => 2, :three => 3 }

  # good
  hash = { one: 1, two: 2, three: 3 }

  # bad
  { a: 1, 'b' => 2 }

  # good
  { :a => 1, 'b' => 2 }

  # bad
  hash.has_key"htmlcode">

  heroes = { batman: 'Bruce Wayne', superman: 'Clark Kent' }
  # bad - if we make a mistake we might not spot it right away
  heroes[:batman] # => "Bruce Wayne"
  heroes[:supermann] # => nil

  # good - fetch raises a KeyError making the problem obvious
  heroes.fetch(:supermann)




    在使用 fetch 时，使用第二个参数设置默认值而不是使用自定义的逻辑。


  batman = { name: 'Bruce Wayne', is_evil: false }

  # bad - if we just use || operator with falsy value we won't get the expected result
  batman[:is_evil] || true # => true

  # good - fetch work correctly with falsy values
  batman.fetch(:is_evil, true) # => false




    尽量用 fetch 加区块而不是直接设定默认值。


  batman = { name: 'Bruce Wayne' }

  # bad - if we use the default value, we eager evaluate it
  # so it can slow the program down if done multiple times
  batman.fetch(:powers, get_batman_powers) # get_batman_powers is an expensive call

  # good - blocks are lazy evaluated, so only triggered in case of KeyError exception
  batman.fetch(:powers) { get_batman_powers }




    当你需要从一个 hash 连续的取回一系列的值的时候使用 Hash#values_at。


  # bad
  email = data['email']
  nickname = data['nickname']

  # good
  email, username = data.values_at('email', 'nickname')




    记住, 在 Ruby1.9 中, 哈希的表现不再是无序的. (译者注: Ruby1.9 将会记住元素插入的序列)
    当遍历一个集合的同时, 不要修改这个集合。