# bad - identifier using non-ascii characters
  заплата = 1_000

  # bad - identifier is a Bulgarian word, written with Latin letters (instead of Cyrillic)
  zaplata = 1_000

  # good
  salary = 1_000

 # bad
  :'some symbol'
  :SomeSymbol
  :someSymbol

  someVar = 5

  def someMethod
   ...
  end

  def SomeMethod
   ...
  end

  # good
  :some_symbol

  def some_method
   ...
  end

# bad
  class Someclass
   ...
  end

  class Some_Class
   ...
  end

  class SomeXml
   ...
  end

  # good
  class SomeClass
   ...
  end

  class SomeXML
   ...
  end

  # bad
  SomeConst = 5

  # good
  SOME_CONST = 5

 # bad - there is not matching 'safe' method
  class Person
   def update!
   end
  end

  # good
  class Person
   def update
   end
  end

  # good
  class Person
   def update!
   end

   def update
   end
  end

  class Array
   def flatten_once!
    res = []

    each do |e|
     [*e].each { |f| res << f }
    end

    replace(res)
   end

   def flatten_once
    dup.flatten_once!
   end
  end

  #Combines all elements of enum枚舉 by applying a binary operation, specified by a block or a symbol that names a method or operator.
  # Sum some numbers
  (5..10).reduce(:+)              #=> 45#reduce
  # Same using a block and inject
  (5..10).inject {|sum, n| sum + n }      #=> 45 #inject注入
  # Multiply some numbers
  (5..10).reduce(1, :*)             #=> 151200
  # Same using a block
  (5..10).inject(1) {|product, n| product * n } #=> 151200

  def +(other)
   # body omitted
  end

  # bad
  some_hash.count

  # good
  some_hash.size

  # bad
  all_songs = users.map(&:songs).flatten.uniq

  # good
  all_songs = users.flat_map(&:songs).uniq

  # bad
  array.reverse.each { ... }

  # good
  array.reverse_each { ... }