RuboCopで実現する美しく調和のとれたRubyスクリプト

RuboCopはRubyのコーディング規則確認ツールです

導入

  $ gem install rubocop
  $ rbenv rehash
  $ exec $SHELL

つかってみる

以下、ダックタイピングの写経で使ったduck.rbです。

class Duck
  def quack
    puts "Quaaaaaack!"
  end

  def is_duck?
    true
  end

  def feathers
    puts "The duck has white and gray feathers."
  end
end
 
class Person
  def quack
    puts "The person imitates a duck."
  end

  def is_duck?
    nil
  end
 
  def feathers
    puts "The person takes a feather from the ground and shows it."
  end
end
 
def in_the_forest(duck)
  duck.quack
  printf " *The duck test* : %s\n" % [ duck.is_duck? ? "ture" : "false"]
  duck.feathers
end
 
def game
  donald = Duck.new
  john = Person.new
  in_the_forest donald
  in_the_forest john
end
 
game

これをrubocopに掛けてみると...

$ rubocop duck.rb
Inspecting 1 file
C

Offenses:

duck.rb:1:1: C: Missing top-level class documentation comment.
class Duck
^^^^^
duck.rb:3:10: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
    puts "Quaaaaaack!"
         ^^^^^^^^^^^^^
duck.rb:6:7: C: Rename is_duck? to duck?.
  def is_duck?
      ^^^^^^^^
duck.rb:11:10: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
    puts "The duck has white and gray feathers."
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
duck.rb:14:1: C: Trailing whitespace detected.
duck.rb:15:1: C: Missing top-level class documentation comment.
class Person
^^^^^
duck.rb:17:10: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
    puts "The person imitates a duck."
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
duck.rb:20:7: C: Rename is_duck? to duck?.
  def is_duck?
      ^^^^^^^^
duck.rb:23:1: C: Trailing whitespace detected.
duck.rb:25:10: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
    puts "The person takes a feather from the ground and shows it."
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
duck.rb:28:1: C: Trailing whitespace detected.
duck.rb:31:36: C: Favor format over String#%.
  printf " *The duck test* : %s\n" % [ duck.is_duck? ? "ture" : "false"]
                                   ^
duck.rb:31:39: C: Space inside square brackets detected.
  printf " *The duck test* : %s\n" % [ duck.is_duck? ? "ture" : "false"]
                                      ^
duck.rb:31:56: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
  printf " *The duck test* : %s\n" % [ duck.is_duck? ? "ture" : "false"]
                                                       ^^^^^^
duck.rb:31:65: C: Prefer single-quoted strings when you don't need string interpolation or special symbols.
  printf " *The duck test* : %s\n" % [ duck.is_duck? ? "ture" : "false"]
                                                                ^^^^^^^
duck.rb:34:1: C: Trailing whitespace detected.
duck.rb:41:1: C: Trailing whitespace detected.

1 file inspected, 17 offenses detected

...こ、これは便利ですね（白目