Rubyでコレクションを書くためのガイド

  # 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]

  # 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?(:test)
  hash.has_value?(value)

  # good
  hash.key?(:test)
  hash.value?(value)

  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)

  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

  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 }

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

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