title
Ruby Style Guide

这边不再更新，整合到自己的笔记里面了：notes/misc/ruby-style-guide.md

Prelude

Role models are important.
-- Officer Alex J. Murphy / RoboCop

One thing has always bothered me as a Ruby developer—Python developers have a great programming style reference (PEP-8) and we never got an official guide, documenting Ruby coding style and best practices. And I do believe that style matters. I also believe that a great hacker community, such as Ruby has, should be quite capable of producing this coveted document.

This guide started its life as our internal company Ruby coding guidelines (written by yours truly). At some point I decided that the work I was doing might be interesting to members of the Ruby community in general and that the world had little need for another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.

Since the inception of the guide I've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.

By the way, if you're into Rails you might want to check out the complementary Ruby on Rails Style Guide.

The Ruby Style Guide

This Ruby style guide recommends best practices so that real-world Ruby programmers can write code that can be maintained by other real-world Ruby programmers. A style guide that reflects real-world usage gets used, while a style guide that holds to an ideal that has been rejected by the people it is supposed to help risks not getting used at all—no matter how good it is.

The guide is separated into several sections of related rules. I've tried to add the rationale behind the rules (if it's omitted I've assumed it's pretty obvious).

I didn't come up with all the rules out of nowhere—they are mostly based on my extensive career as a professional software engineer, feedback and suggestions from members of the Ruby community and various highly regarded Ruby programming resources, such as "Programming Ruby" and "The Ruby Programming Language".

There are some areas in which there is no clear consensus in the Ruby community regarding a particular style (like string literal quoting, spacing inside hash literals, dot position in multi-line method chaining, etc.). In such scenarios all popular styles are acknowledged and it's up to you to pick one and apply it consistently.

This style guide evolves over time as additional conventions are identified and past conventions are rendered obsolete by changes in Ruby itself.

Many projects have their own coding style guidelines (often derived from this guide). In the event of any conflicts, such project-specific guides take precedence for that project.

You can generate a PDF or an HTML copy of this guide using Pandoc.

RuboCop is a code analyzer, based on this style guide.

Translations of the guide are available in the following languages:

Source Code Layout

Nearly everybody is convinced that every style but their own is ugly and unreadable. Leave out the "but their own" and they're probably right...
-- Jerry Coffin (on indentation)

• Use UTF-8 as the source file encoding.

• Use two spaces per indentation level (aka soft tabs). No hard tabs.

  # bad - four spaces
  def some_method
      do_something
  end
  
  # good
  def some_method
    do_something
  end

• Use Unix-style line endings. (*BSD/Solaris/Linux/macOS users are covered by default, Windows users have to be extra careful.)

  • If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:

    $ git config --global core.autocrlf true

• Don't use ; to separate statements and expressions. As a corollary—use one expression per line.

  corollary 推论，必然

  # bad
  puts 'foobar'; # superfluous semicolon
  
  puts 'foo'; puts 'bar' # two expressions on the same line
  
  # good
  puts 'foobar'
  
  puts 'foo'
  puts 'bar'
  
  puts 'foo', 'bar' # this applies to puts in particular

• Prefer a single-line format for class definitions with no body.

  没有内容的 class 定义，用 ClassName = Class.new(parent)

  # bad
  class FooError < StandardError
  end
  
  # okish
  class FooError < StandardError; end
  
  # good
  FooError = Class.new(StandardError)

• Avoid single-line methods. Although they are somewhat popular in the wild, there are a few peculiarities about their definition syntax that make their use undesirable. At any rate—there should be no more than one expression in a single-line method.

  有内容的 function 定义，不要写成 one-liner

  # bad
  def too_much; something; something_else; end
  
  # okish - notice that the first ; is required
  def no_braces_method; body end
  
  # okish - notice that the second ; is optional
  def no_braces_method; body; end
  
  # okish - valid syntax, but no ; makes it kind of hard to read
  def some_method() body end
  
  # good
  def some_method
    body
  end

  One exception to the rule are empty-body methods.

  # good
  def no_op; end

• Use spaces around operators, after commas, colons and semicolons. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code. 特么多加点空格……

  sum = 1 + 2
  a, b = 1, 2
  class FooError < StandardError; end

  The only exception, regarding operators, is the exponent operator: 除了指数符号（其实 unary 符号都不应该加空格，比如 !）

  # bad
  e = M * c ** 2
  
  # good
  e = M * c**2

• No spaces after (, [ or before ], ). Use spaces around { and before }. 不要给 method param 那左右加上空格……太过…… 函数 block 则加上。

  # bad
  some( arg ).other
  [ 1, 2, 3 ].each{|e| puts e}
  
  # good
  some(arg).other
  [1, 2, 3].each { |e| puts e }

  { and } deserve a bit of clarification, since they are used for block and hash literals, as well as string interpolation.

  For hash literals two styles are considered acceptable. The first variant is slightly more readable (and arguably more popular in the Ruby community in general). The second variant has the advantage of adding visual difference between block and hash literals. Whichever one you pick—apply it consistently.

  # good - space after { and before }
  { one: 1, two: 2 }
  
  # good - no space after { and before }
  {one: 1, two: 2}

  With interpolated expressions, there should be no padded-spacing inside the braces. 字符串模板里面就别弄那么多空格了……

  # bad
  "From: #{ user.first_name }, #{ user.last_name }"
  
  # good
  "From: #{user.first_name}, #{user.last_name}"

• No space after !. 这个其实和 ** 应该弄到一起说。

  # bad
  ! something
  
  # good
  !something

• No space inside range literals.

  # bad
  1 .. 3
  'a' ... 'z'
  
  # good
  1..3
  'a'...'z'

• Indent when as deep as case. This is the style established in both "The Ruby Programming Language" and "Programming Ruby". 这个现在 C++ 也是这样的风格。其实是在在像 if elseif 看齐。

  # bad
  case
    when song.name == 'Misty'
      puts 'Not again!'
    when song.duration > 120
      puts 'Too long!'
    when Time.now.hour > 21
      puts "It's too late"
    else
      song.play
  end
  
  # good
  case
  when song.name == 'Misty'
    puts 'Not again!'
  when song.duration > 120
    puts 'Too long!'
  when Time.now.hour > 21
    puts "It's too late"
  else
    song.play
  end

• When assigning the result of a conditional expression to a variable, preserve the usual alignment of its branches.

  # bad - pretty convoluted
  kind = case year
  when 1850..1889 then 'Blues'
  when 1890..1909 then 'Ragtime'
  when 1910..1929 then 'New Orleans Jazz'
  when 1930..1939 then 'Swing'
  when 1940..1950 then 'Bebop'
  else 'Jazz'
  end
  
  result = if some_cond
    calc_something
  else
    calc_something_else
  end
  
  # good - it's apparent what's going on
  kind = case year
         when 1850..1889 then 'Blues'
         when 1890..1909 then 'Ragtime'
         when 1910..1929 then 'New Orleans Jazz'
         when 1930..1939 then 'Swing'
         when 1940..1950 then 'Bebop'
         else 'Jazz'
         end
  
  result = if some_cond
             calc_something
           else
             calc_something_else
           end
  
  # good (and a bit more width efficient)
  kind =
    case year
    when 1850..1889 then 'Blues'
    when 1890..1909 then 'Ragtime'
    when 1910..1929 then 'New Orleans Jazz'
    when 1930..1939 then 'Swing'
    when 1940..1950 then 'Bebop'
    else 'Jazz'
    end
  
  result =
    if some_cond
      calc_something
    else
      calc_something_else
    end

• Use empty lines between method definitions and also to break up methods into logical paragraphs internally. 其实就是逻辑分块……

  def some_method
    data = initialize(options)
  
    data.manipulate!
  
    data.result
  end
  
  def some_method
    result
  end

  不过不要在 class 和 function 的第一行就空行。

• Don't use several empty lines in a row. 编辑器也不同意啊！

  # bad - It has two empty lines.
  some_method
  
  
  some_method
  
  # good
  some_method
  
  some_method

• Use empty lines around access modifiers. 这个就相当于定义了自带 getter 和 setters 的变量。 比如这里 attr_reader 就可以读取 @foo 这个内部变量。

  # bad
  class Foo
    attr_reader :foo
    def foo
      # do something...
    end
  end
  
  # good
  class Foo
    attr_reader :foo
  
    def foo
      # do something...
    end
  end

• Don't use empty lines around method, class, module, block bodies. 这些空行不必要……

  # bad
  class Foo
  
    def foo
  
      begin
  
        do_something do
  
          something
  
        end
  
      rescue
  
        something
  
      end
  
    end
  
  end
  
  # good
  class Foo
    def foo
      begin
        do_something do
          something
        end
      rescue
        something
      end
    end
  end

• Avoid comma after the last parameter in a method call, especially when the parameters are not on separate lines. 我就喜欢这样……话说特别讨厌 JSON 文本得列表不允许最后元素后面加个“,”， 不过从好看的角度，确实应该去掉。

  # bad - easier to move/add/remove parameters, but still not preferred
  some_method(
    size,
    count,
    color,
  )
  
  # bad
  some_method(size, count, color, )
  
  # good
  some_method(size, count, color)

• Use spaces around the = operator when assigning default values to method parameters:

  # bad
  def some_method(arg1=:default, arg2=nil, arg3=[])
    # do something...
  end
  
  # good
  def some_method(arg1 = :default, arg2 = nil, arg3 = [])
    # do something...
  end

  While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).

• Avoid line continuation \ where not required. In practice, avoid using line continuations for anything but string concatenation. 其实这和英语里列表说“1) blah blah and 2) blah blah”类似。

  # bad
  result = 1 - \
           2
  
  # good (but still ugly as hell)
  result = 1 \
           - 2
  
  long_string = 'First part of the long string' \
                ' and second part of the long string'

• Adopt a consistent multi-line method chaining style. There are two popular styles in the Ruby community, both of which are considered good—leading . (Option A) and trailing . (Option B).

  • (Option A) When continuing a chained method invocation on another line keep the . on the second line.

    # bad - need to consult first line to understand second line
    one.two.three.
      four
    
    # good - it's immediately clear what's going on the second line
    one.two.three
      .four

  • (Option B) When continuing a chained method invocation on another line, include the . on the first line to indicate that the expression continues.

    # bad - need to read ahead to the second line to know that the chain continues
    one.two.three
      .four
    
    # good - it's immediately clear that the expression continues beyond the first line
    one.two.three.
      four

  A discussion on the merits of both alternative styles can be found here.

• Align the parameters of a method call if they span more than one line. When aligning parameters is not appropriate due to line-length constraints, single indent for the lines after the first is also acceptable. 我还是喜欢 8 个空格（两倍于常规 indent）的对齐。或者直接对齐到括弧。

  # starting point (line is too long)
  def send_mail(source)
    Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text)
  end
  
  # bad (double indent)
  # 说实话在 C++ 里面我就喜欢这样 align
  def send_mail(source)
    Mailer.deliver(
        to: 'bob@example.com',
        from: 'us@example.com',
        subject: 'Important message',
        body: source.text)
  end
  
  # good
  # 当然这样也不错
  def send_mail(source)
    Mailer.deliver(to: 'bob@example.com',
                   from: 'us@example.com',
                   subject: 'Important message',
                   body: source.text)
  end
  
  # good (normal indent)
  def send_mail(source)
    Mailer.deliver(
      to: 'bob@example.com',
      from: 'us@example.com',
      subject: 'Important message',
      body: source.text
    )
  end

• Align the elements of array literals spanning multiple lines. 第二种好看。

  # bad - single indent
  menu_item = ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
    'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']
  
  # good
  # 我最喜欢这样得
  menu_item = [
    'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
    'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam'
  ]
  
  # good
  menu_item =
    ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
     'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']

• Add underscores to large numeric literals to improve their readability. 这是 Ruby 独有得优势（好像 Perl 也有），利用之。

  # bad - how many 0s are there?
  num = 1000000
  
  # good - much easier to parse for the human brain
  num = 1_000_000

• Prefer smallcase letters for numeric literal prefixes. 0o for octal, 0x for hexadecimal and 0b for binary. Do not use 0d prefix for decimal literals. 在我看来，0o 这样用确实比较少见……不过确实不错。

  # bad
  num = 01234
  num = 0O1234
  num = 0X12AB
  num = 0B10101
  num = 0D1234
  num = 0d1234
  
  # good - easier to separate digits from the prefix
  num = 0o1234
  num = 0x12AB
  num = 0b10101
  num = 1234

• Use Rdoc and its conventions for API documentation. Don't put an empty line between the comment block and the def.

• Limit lines to 80 characters.

• Avoid trailing whitespace.

• End each file with a newline. 这个是为啥？

• Don't use block comments. They cannot be preceded by whitespace and are not as easy to spot as regular comments. 用单行得注释，chenshuo 还说过这样的注释在 diff 里还更直观。

  # bad
  =begin
  comment line
  another comment line
  =end
  
  # good
  # comment line
  # another comment line

Syntax

• Use :: only to reference constants(this includes classes and modules) and constructors (like Array() or Nokogiri::HTML()). Do not use :: for regular method invocation. :: 只用来构造 instance，或者获取常量（反正是用来得到一个值/对象）。 不要向 C++ 里面那样，invoke method（静态）就用这个。

  # bad
  SomeClass::some_method
  some_object::some_method
  
  # good
  SomeClass.some_method
  some_object.some_method
  SomeModule::SomeClass::SOME_CONST
  SomeModule::SomeClass()

• Use def with parentheses when there are parameters. Omit the parentheses when the method doesn't accept any parameters. 没有参数就省略括弧。

  # bad
  def some_method()
    # body omitted
  end
  
  # good
  def some_method
    # body omitted
  end
  
  # bad
  def some_method_with_parameters param1, param2
    # body omitted
  end
  
  # good
  def some_method_with_parameters(param1, param2)
    # body omitted
  end

• Use parentheses around the arguments of method invocations, especially if the first argument begins with an open parenthesis (, as in f((3 + 2) + 1). 函数调用有参数的时候，还是加上括弧把。 这部分都很有意思。:hearts:

  # bad
  x = Math.sin y
  # good
  x = Math.sin(y)
  
  # bad
  array.delete e
  # good
  array.delete(e)
  
  # bad
  temperance = Person.new 'Temperance', 30
  # good
  temperance = Person.new('Temperance', 30)

  Always omit parentheses for 一定不能要括弧

  • Method calls with no arguments: 没参数就不要括弧了。

    # bad
    Kernel.exit!()
    2.even?()
    fork()
    'test'.upcase()
    
    # good
    Kernel.exit!
    2.even?
    fork
    'test'.upcase

  • Methods that are part of an internal DSL (e.g., Rake, Rails, RSpec): DSL 就不要按照这个规则来了。

    # bad
    validates(:name, presence: true)
    # good
    validates :name, presence: true

  • Methods that have "keyword" status in Ruby: ？？这是啥？？

    class Person
      # bad
      attr_reader(:name, :age)
      # good
      attr_reader :name, :age
    
      # body omitted
    end

  Can omit parentheses for 可以不要

  • Methods that have "keyword" status in Ruby, but are not declarative:

    # good
    puts(temperance.age)
    system('ls')
    # also good
    puts temperance.age
    system 'ls'

• Define optional arguments at the end of the list of arguments. Ruby has some unexpected results when calling methods that have optional arguments at the front of the list. 这个在 C++ 里面直接是不允许得。

  # bad
  def some_method(a = 1, b = 2, c, d)
    puts "#{a}, #{b}, #{c}, #{d}"
  end
  
  some_method('w', 'x') # => '1, 2, w, x'
  some_method('w', 'x', 'y') # => 'w, 2, x, y'
  some_method('w', 'x', 'y', 'z') # => 'w, x, y, z'
  
  # good
  def some_method(c, d, a = 1, b = 2)
    puts "#{a}, #{b}, #{c}, #{d}"
  end
  
  some_method('w', 'x') # => '1, 2, w, x'
  some_method('w', 'x', 'y') # => 'y, 2, w, x'
  some_method('w', 'x', 'y', 'z') # => 'y, z, w, x'

• Avoid the use of parallel assignment for defining variables. Parallel assignment is allowed when it is the return of a method call, used with the splat operator, or when used to swap variable assignment. Parallel assignment is less readable than separate assignment. 定义的时候不要这么玩。只有在赋值的时候才用 parallel assignment。

  # bad
  a, b, c, d = 'foo', 'bar', 'baz', 'foobar'
  
  # good
  a = 'foo'
  b = 'bar'
  c = 'baz'
  d = 'foobar'
  
  # good - swapping variable assignment
  # Swapping variable assignment is a special case because it will allow you to
  # swap the values that are assigned to each variable.
  a = 'foo'
  b = 'bar'
  
  a, b = b, a
  puts a # => 'bar'
  puts b # => 'foo'
  
  # good - method return
  def multi_return
    [1, 2]
  end
  
  first, second = multi_return
  
  # good - use with splat
  first, *list = [1, 2, 3, 4] # first => 1, list => [2, 3, 4]
  
  hello_array = *'Hello' # => ["Hello"]
  
  a = *(1..3) # => [1, 2, 3]

• Avoid the use of unnecessary trailing underscore variables during parallel assignment. Named underscore variables are to be preferred over underscore variables because of the context that they provide. Trailing underscore variables are necessary when there is a splat variable defined on the left side of the assignment, and the splat variable is not an underscore. 多余的不要，加上逗号就行。

  # bad
  foo = 'one,two,three,four,five'
  # Unnecessary assignment that does not provide useful information
  first, second, _ = foo.split(',')
  first, _, _ = foo.split(',')
  first, *_ = foo.split(',')
  
  # good
  # 没必要用 `_`
  foo = 'one,two,three,four,five'
  # The underscores are needed to show that you want all elements
  # except for the last number of underscore elements
  *beginning, _ = foo.split(',')
  *beginning, something, _ = foo.split(',')
  
  a, = foo.split(',')
  a, b, = foo.split(',')
  # Unnecessary assignment to an unused variable, but the assignment
  # provides us with useful information.
  # 加个名字说明是啥
  first, _second = foo.split(',')
  first, _second, = foo.split(',')
  first, *_ending = foo.split(',')

• Do not use for, unless you know exactly why. Most of the time iterators should be used instead. for is implemented in terms of each (so you're adding a level of indirection), but with a twist—for doesn't introduce a new scope (unlike each) and variables defined in its block will be visible outside it. each 的作用域似乎更好用？

  arr = [1, 2, 3]
  
  # bad
  for elem in arr do
    puts elem
  end
  
  # note that elem is accessible outside of the for loop
  elem # => 3
  
  # good
  arr.each { |elem| puts elem }
  
  # elem is not accessible outside each's block
  elem # => NameError: undefined local variable or method `elem'

• Do not use then for multi-line if/unless. then 只在一行的时候用（不要用 ;）。

  # bad
  if some_condition then
    # body omitted
  end
  
  # good
  if some_condition
    # body omitted
  end

• Always put the condition on the same line as the if/unless in a multi-line conditional. 第一行也有有 cond

  # bad
  if
    some_condition
    do_something
    do_something_else
  end
  
  # good
  if some_condition
    do_something
    do_something_else
  end

• Favor the ternary operator(?:) over if/then/else/end constructs. It's more common and obviously more concise. 三元运算符看上去简洁点。

  # bad
  result = if some_condition then something else something_else end
  
  # good
  result = some_condition ? something : something_else

• Use one expression per branch in a ternary operator. This also means that ternary operators must not be nested. Prefer if/else constructs in these cases. 复杂了，就不要用 ternary 运算符，直接 if else 更明白点。

  # bad
  some_condition ? (nested_condition ? nested_something : nested_something_else) : something_else
  
  # good
  if some_condition
    nested_condition ? nested_something : nested_something_else
  else
    something_else
  end

• Do not use if x; .... Use the ternary operator instead.

  # bad
  result = if some_condition; something else something_else end
  
  # good
  result = some_condition ? something : something_else

• Leverage the fact that if and case are expressions which return a result. 这个和大多数编程语言不一样，因为 ruby 的 if else 也是 expression，while 别 的语言都只算 statement。在 Ruby 里，一个表达式（expression）是有返回值的。

  # bad
  if condition
    result = x
  else
    result = y
  end
  
  # good
  result =
    if condition
      x
    else
      y
    end

• Use when x then ... for one-line cases. The alternative syntax when x: ... has been removed as of Ruby 1.9.

• Do not use when x; .... See the previous rule.

• Use ! instead of not.

  # bad - parentheses are required because of op precedence
  x = (not something)
  
  # good
  x = !something

• Avoid the use of !!. 这个在 JS 里面也有用。

  !! converts a value to boolean, but you don't need this explicit conversion in the condition of a control expression; using it only obscures your intention. If you want to do a nil check, use nil? instead.

  # bad
  x = 'test'
  # obscure nil check
  if !!x
    # body omitted
  end
  
  # good
  x = 'test'
  if x
    # body omitted
  end

• The and and or keywords are banned. The minimal added readability is just not worth the high probability of introducing subtle bugs. For boolean expressions, always use && and || instead. For flow control, use if and unless; && and || are also acceptable but less clear. 不要用 and 和 or 之类的太英语的关键词……

  # bad
  # boolean expression
  ok = got_needed_arguments and arguments_are_valid
  
  # control flow
  document.save or fail(RuntimeError, "Failed to save document!")
  
  # good
  # boolean expression
  ok = got_needed_arguments && arguments_are_valid
  
  # control flow
  fail(RuntimeError, "Failed to save document!") unless document.save
  
  # ok
  # control flow
  document.save || fail(RuntimeError, "Failed to save document!")

• Avoid multi-line ?: (the ternary operator); use if/unless instead. 这个不是说了么……

• Favor modifier if/unless usage when you have a single-line body. Another good alternative is the usage of control flow &&/||. 如果只有一个语句，就用 modifier。

  # bad
  if some_condition
    do_something
  end
  
  # good
  do_something if some_condition
  
  # another good option
  some_condition && do_something

• Avoid modifier if/unless usage at the end of a non-trivial multi-line block. 后置的 if 还是只适合 one-liner。

  # bad
  10.times do
    # multi-line body omitted
  end if some_condition
  
  # good
  if some_condition
    10.times do
      # multi-line body omitted
    end
  end

• Avoid nested modifier if/unless/while/until usage. Favor &&/|| if appropriate. 第一种写法也太凶残了……

  # bad
  do_something if other_condition if some_condition
  
  # good
  do_something if some_condition && other_condition

• Favor unless over if for negative conditions (or control flow ||). 话说用 unless 的时候，我总是在心里自己 if not 了一下……

  # bad
  do_something if !some_condition
  
  # bad
  do_something if not some_condition
  
  # good
  do_something unless some_condition
  
  # another good option
  some_condition || do_something

• Do not use unless with else. Rewrite these with the positive case first. unless 只要和一个跟……（这个好像不是风格，而是思考的哲学。） （不过有时候就是 unless ... else ... 才好用呢……）

  # bad
  unless success?
    puts 'failure'
  else
    puts 'success'
  end
  
  # good
  if success?
    puts 'success'
  else
    puts 'failure'
  end

• Don't use parentheses around the condition of a control expression. if 后面不需要括弧。

  # bad
  if (x > 10)
    # body omitted
  end
  
  # good
  if x > 10
    # body omitted
  end

  Note that there is an exception to this rule, namely "safe assignment in condition"

  # bad (+ a warning)
  if v = array.grep(/foo/)
      do_something(v)
      # some code
  end

• Do not use while/until condition do for multi-line while/until. 这个和 if ... then 一样，只有 one-liner 加上 then。

  # bad
  while x > 5 do
    # body omitted
  end
  
  until x > 5 do
    # body omitted
  end
  
  # good
  while x > 5
    # body omitted
  end
  
  until x > 5
    # body omitted
  end

• Favor modifier while/until usage when you have a single-line body. 话说这样确实没错，不过很多时候你不太清楚这个 body 是不是 single-line 就能搞定。所以啊……乖乖写成 while ... end 最好。还可以扩展。 只有在极其 sure 只有一个 single-line bode 的时候，才用后置。（我真是机智）

  # bad
  while some_condition
    do_something
  end
  
  # good
  do_something while some_condition

• Favor until over while for negative conditions. 其实这都可以解释为“请用直观的那个关键词！”…… 不要特么脑子拎不清瞎用反转。

  # bad
  do_something while !some_condition
  
  # good
  do_something until some_condition

• Use Kernel#loop instead of while/until when you need an infinite loop. 这个函数不错……loop 就是死循环。推荐加上 do。

  # bad
  while true
    do_something
  end
  
  until false
    do_something
  end
  
  # good
  loop do
    do_something
  end

• Use Kernel#loop with break rather than begin/end/until or begin/end/while for post-loop tests.

  # bad
  begin
    puts val
    val += 1
  end while val < 0
  
  # good
  loop do
    puts val
    val += 1
    break unless val < 0
  end

• Omit the outer braces around an implicit options hash. hash 可以自动 boxing 好，所以不用自己加上 "{}"（不过我感觉加了也挺好……）

  # bad
  user.set({ name: 'John', age: 45, permissions: { read: true } })
  
  # good
  user.set(name: 'John', age: 45, permissions: { read: true })

• Omit both the outer braces and parentheses for methods that are part of an internal DSL. 这样看起来清爽点，不要一般函数调用，其他的话……也没啥……

  class Person < ActiveRecord::Base
    # bad
    validates(:name, { presence: true, length: { within: 1..10 } })
  
    # good
    validates :name, presence: true, length: { within: 1..10 }
  end

  之前说了有参数的话要加上括弧，现在呢……嗯……如果参数是一个 hash，就不要括弧了……

• Use the proc invocation shorthand when the invoked method is the only operation of a block. 用 symbol 前置 & 的方式来 invocate 一个 proc。

  # bad
  names.map { |name| name.upcase }
  
  # good
  names.map(&:upcase)

• Prefer {...} over do...end for single-line blocks. Avoid using {...} for multi-line blocks (multi-line chaining is always ugly). Always use do...end for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs). Avoid do...end when chaining. 这个我在 Learning Ruby 的笔记里也总结了。（我好机智……） 外，可以 chain 就是好。

  names = %w[Bozhidar Steve Sarah]
  
  # bad
  names.each do |name|
    puts name
  end
  
  # good
  names.each { |name| puts name }
  
  # bad
  names.select do |name|
    name.start_with?('S')
  end.map { |name| name.upcase }
  
  # good
  names.select { |name| name.start_with?('S') }.map(&:upcase)

  Some will argue that multi-line chaining would look OK with the use of {...}, but they should ask themselves—is this code really readable and can the blocks' contents be extracted into nifty methods?

  话说这个逻辑我没看懂……我要是那个“some”的话，我就要说“你这是逻辑上耍流氓！”。

• Consider using explicit block argument to avoid writing block literal that just passes its arguments to another block. Beware of the performance impact, though, as the block gets converted to a Proc. 只是一个封装，导出一个啥，实在太 low。为哈不直接 take 一个 block，然后处理它呢？

  require 'tempfile'
  
  # bad
  def with_tmp_dir
    Dir.mktmpdir do |tmp_dir|
      Dir.chdir(tmp_dir) { |dir| yield dir }  # block just passes arguments
    end
  end
  
  # good
  def with_tmp_dir(&block)
    Dir.mktmpdir do |tmp_dir|
      Dir.chdir(tmp_dir, &block)
    end
  end
  
  with_tmp_dir do |dir|
    puts "dir is accessible as a parameter and pwd is set: #{dir}"
  end

• Avoid return where not required for flow of control. return 要戒。

  # bad
  def some_method(some_arr)
    return some_arr.size
  end
  
  # good
  def some_method(some_arr)
    some_arr.size
  end

• Avoid self where not required. (It is only required when calling a self write accessor, methods named after reserved words, or overloadable operators.)

  # bad
  def ready?
    if self.last_reviewed_at > self.last_updated_at
      self.worker.update(self.content, self.options)
      self.status = :in_progress
    end
    self.status == :verified
  end
  
  # good
  def ready?
    if last_reviewed_at > last_updated_at
      worker.update(content, options)
      self.status = :in_progress
    end
    status == :verified
  end

• As a corollary, avoid shadowing methods with local variables unless they are both equivalent. 避免外面来一个变量把内部的变量给 shadow 了。

  class Foo
    attr_accessor :options
  
    # ok
    def initialize(options)
      self.options = options
      # both options and self.options are equivalent here
    end
  
    # bad
    def do_something(options = {})
      unless options[:when] == :later
        output(self.options[:message])
      end
    end
  
    # good
    def do_something(params = {})
      unless params[:when] == :later
        output(options[:message])
      end
    end
  end

• Don't use the return value of = (an assignment) in conditional expressions unless the assignment is wrapped in parentheses. This is a fairly popular idiom among Rubyists that's sometimes referred to as safe assignment in condition. 这个上面说了……

  # bad (+ a warning)
  if v = array.grep(/foo/)
    do_something(v)
    # some code
  end
  
  # good (MRI would still complain, but RuboCop won't)
  if (v = array.grep(/foo/))
    do_something(v)
    # some code
  end
  
  # good
  v = array.grep(/foo/)
  if v
    do_something(v)
    # some code
  end

• Use shorthand self assignment operators whenever applicable. 这个是各种语言都使用的规范。

  # bad
  x = x + y
  x = x * y
  x = x**y
  x = x / y
  x = x || y
  x = x && y
  
  # good
  x += y
  x *= y
  x **= y
  x /= y
  x ||= y
  x &&= y

• Use ||= to initialize variables only if they're not already initialized.

  # bad
  name = name ? name : 'Bozhidar'
  
  # bad
  name = 'Bozhidar' unless name
  
  # good - set name to 'Bozhidar', only if it's nil or false
  name ||= 'Bozhidar'

• Don't use ||= to initialize boolean variables. (Consider what would happen if the current value happened to be false.) :nil? 有点意思。

  # bad - would set enabled to true even if it was false
  enabled ||= true
  
  # good
  enabled = true if enabled.nil?

• Use &&= to preprocess variables that may or may not exist. Using &&= will change the value only if it exists, removing the need to check its existence with if. 这个牛逼了……从来都是一个 chain 地看是否有这个东西……这样就不用写得很啰嗦了。

  # bad
  if something
    something = something.downcase
  end
  
  # bad
  something = something ? something.downcase : nil
  
  # ok
  something = something.downcase if something
  
  # good
  something = something && something.downcase
  
  # better
  something &&= something.downcase

• Avoid explicit use of the case equality operator ===. As its name implies it is meant to be used implicitly by case expressions and outside of them it yields some pretty confusing code. 不要自己写“===”，这个东西在 case when 的时候用就可以了。

  # bad
  Array === something
  (1..100) === 7
  /something/ === some_string
  
  # good
  something.is_a?(Array)
  (1..100).include?(7)
  some_string =~ /something/

• Do not use eql? when using == will do. The stricter comparison semantics provided by eql? are rarely needed in practice. eql? 这东西没啥实际用处，根本没有应用机会。

  # bad - eql? is the same as == for strings
  'ruby'.eql? some_str
  
  # good
  'ruby' == some_str
  1.0.eql? x # eql? makes sense here if want to differentiate between Integer and Float 1

• Avoid using Perl-style special variables (like $:, $;, etc. ). They are quite cryptic （含义模糊的） and their use in anything but one-liner scripts is discouraged. Use the human-friendly aliases provided by the English library.

  # bad
  $:.unshift File.dirname(__FILE__)                   # 这个太特么常见了。
  
  # good
  require 'English'
  $LOAD_PATH.unshift File.dirname(__FILE__)

  上面的代码就是形成一个 $PATH，把当前目录 prepend 到里面。

• Do not put a space between a method name and the opening parenthesis. 为啥？因为这样特么有歧义啊！ 这根本不是 good 和 bad 的问题，这是 right 和 wrong 的问题。

  # bad
  f (3 + 2) + 1
  
  # good
  f(3 + 2) + 1

• Always run the Ruby interpreter with the -w option so it will warn you if you forget either of the rules above! 加上这个“-w”选项，就可以提示你。有点类似 JavaScript 的“use strict;”。

• Do not use nested method definitions, use lambda instead. Nested method definitions actually produce methods in the same scope (e.g. class) as the outer method. Furthermore, the "nested method" will be redefined every time the method containing its definition is invoked. 不要嵌套定义 method，如果你的函数只在局部用一两次，那就用 lambda。

  # bad
  def foo(x)
    def bar(y)
      # body omitted
    end
  
    bar(x)
  end
  
  # good - the same as the previous, but no bar redefinition on every foo call
  def bar(y)
    # body omitted
  end
  
  def foo(x)
    bar(x)
  end
  
  # also good
  def foo(x)
    bar = ->(y) { ... }
    bar.call(x)
  end

• Use the new lambda literal syntax for single line body blocks. Use the lambda method for multi-line blocks. 一行的 method，用 ->（stabby），多行的用 lambda 关键字。

  # bad
  l = lambda { |a, b| a + b }
  l.call(1, 2)
  
  # correct, but looks extremely awkward
  l = ->(a, b) do
    tmp = a * 7
    tmp * b / 50
  end
  
  # good
  l = ->(a, b) { a + b }
  l.call(1, 2)
  
  l = lambda do |a, b|
    tmp = a * 7
    tmp * b / 50
  end

• Don't omit the parameter parentheses when defining a stabby lambda with parameters. 虽然 lambda 可以省略括弧，但是不推荐。请加上。 只有没有参数的时候，不要括弧。

  # bad
  l = ->x, y { something(x, y) }
  
  # good
  l = ->(x, y) { something(x, y) }

• Omit the parameter parentheses when defining a stabby lambda with no parameters. 如果没有参数的话，那就不要括弧。

  # bad
  l = ->() { something }
  
  # good
  l = -> { something }

• Prefer proc over Proc.new. 用 proc 而不是 Proc.new，两种用法一样的。

  # bad
  p = Proc.new { |n| puts n }
  
  # good
  p = proc { |n| puts n }

• Prefer proc.call() over proc[] or proc.() for both lambdas and procs. proc.call 更加清晰。

  # bad - looks similar to Enumeration access
  l = ->(v) { puts v }
  l[1]
  
  # also bad - uncommon syntax
  l = ->(v) { puts v }
  l.(1)
  
  # good
  l = ->(v) { puts v }
  l.call(1)

• Prefix with _ unused block parameters and local variables. It's also acceptable to use just _ (although it's a bit less descriptive). This convention is recognized by the Ruby interpreter and tools like RuboCop and will suppress their unused variable warnings. 可以用“”前缀标记局部没用到的变量。 只用“”的话，不够清晰，但也 Okay，不过还是推荐加上一个说明。

  # bad
  result = hash.map { |k, v| v + 1 }
  
  def something(x)
    unused_var, used_var = something_else(x)
    # some code
  end
  
  # good
  result = hash.map { |_k, v| v + 1 }
  
  def something(x)
    _unused_var, used_var = something_else(x)
    # some code
  end
  
  # good
  result = hash.map { |_, v| v + 1 }
  
  def something(x)
    _, used_var = something_else(x)
    # some code
  end

• Use $stdout/$stderr/$stdin instead of STDOUT/STDERR/STDIN. STDOUT/STDERR/STDIN are constants, and while you can actually reassign (possibly to redirect some stream) constants in Ruby, you'll get an interpreter warning if you do so.

  $stdout 等三个常用 fd 要比 STDOUT 这三个类似的常量好，因为后者 可能被重新赋值了。这是 error-prone。

• Use warn instead of $stderr.puts. Apart from being more concise and clear, warn allows you to suppress warnings if you need to (by setting the warn level to 0 via -W0). 错误输出用 warn。

• Favor the use of sprintf and its alias format over the fairly cryptic String#% method. 虽然 Ruby 提供 str%array 的方法来 format 字符串，还是推荐用 sprintf 或者 format。

  # bad
  '%d %d' % [20, 10]
  # => '20 10'
  
  # good
  sprintf('%d %d', 20, 10)
  # => '20 10'
  
  # good
  sprintf('%<first>d %<second>d', first: 20, second: 10)
  # => '20 10'
  
  format('%d %d', 20, 10)
  # => '20 10'
  
  # good
  format('%<first>d %<second>d', first: 20, second: 10)
  # => '20 10'

• When using named format string tokens, favor %<name>s over %{name} because it encodes information about the type of the value.

  # bad
  format('Hello, %{name}', name: 'John')
  
  # good
  format('Hello, %<name>s', name: 'John')

• Favor the use of Array#join over the fairly cryptic Array#* with a string argument. 用 join 来 join，而不用蛋疼的 * 字符。

  # bad
  %w[one two three] * ', '
  # => 'one, two, three'
  
  # good
  %w[one two three].join(', ')
  # => 'one, two, three'

• Use Array() instead of explicit Array check or [*var], when dealing with a variable you want to treat as an Array, but you're not certain it's an array. **Array(input) 总是输出一个 Array。**十分好用的样子。

  # bad
  paths = [paths] unless paths.is_a? Array
  paths.each { |path| do_something(path) }
  
  # bad (always creates a new Array instance)
  [*paths].each { |path| do_something(path) }
  
  # good (and a bit more readable)
  Array(paths).each { |path| do_something(path) }

• Use ranges or Comparable#between? instead of complex comparison logic when possible. 用 between？直接判断区间。

  # bad
  do_something if x >= 1000 && x <= 2000
  
  # good
  do_something if (1000..2000).include?(x)
  
  # good
  do_something if x.between?(1000, 2000)

• Favor the use of predicate methods to explicit comparisons with ==. Numeric comparisons are OK. 能用专业的表达，就不要用自己 naive 的实现拉！

  # bad
  if x % 2 == 0
  end
  
  if x % 2 == 1
  end
  
  if x == nil
  end
  
  # good
  if x.even?
  end
  
  if x.odd?
  end
  
  if x.nil?
  end
  
  if x.zero?
  end
  
  if x == 0
  end

• Don't do explicit non-nil checks unless you're dealing with boolean values. 咋说呢，一般用 if ... 来判断这个东西是不是 nil，如果不是 nil，就可以处理。 除了……如果这个变量本来就是 boolean，这时候，你还是判断一下它是 nil 还 false 为好。

  # bad
  do_something if !something.nil?
  do_something if something != nil
  
  # good
  do_something if something
  
  # good - dealing with a boolean
  def value_set?
    !@some_boolean.nil?
  end

• Avoid the use of BEGIN blocks. 这个东西其实可以用其他的流程避免。 不过我个人挺喜欢，因为逻辑上更加紧凑，你可以把一个循环只处理一次的东西写到里面， 而不是放在外面。

  不过看上去，这里说的是文本 scope 下的 BEGIN，这个……执行顺序太不好掌控了。 （我是说，虽然你知道这个是有顺序的，但还是要自己看看想想，不好不好。好的代码，不需要 担心这担心那，还要人工 check。）

• Do not use END blocks. Use Kernel#at_exit instead. 跟 C 语言一样，注册一个函数。（不过 Ruby 下应该能注册多个。）

  # bad
  END { puts 'Goodbye!' }
  
  # good
  at_exit { puts 'Goodbye!' }

• Avoid the use of flip-flops. 因为有点复杂……可以改成 while，然后 check 状态。

• Avoid use of nested conditionals for flow of control. 这个我写 C++ 就用的这个原则。因为如果总是 if，然后到下一层， 你的代码会越来越宽，看上去很不好。 可以一点一点 check，直接返回。 这样一来，后面可以写得很窄，还保证了它的预设条件是正确的。 嗯……下面也说了，这叫“guard clause”。

  Prefer a guard clause when you can assert invalid data. A guard clause is a conditional statement at the top of a function that bails out as soon as it can.

  # bad
  def compute_thing(thing)
    if thing[:foo]
      update_with_bar(thing[:foo])
      if thing[:foo][:bar]
        partial_compute(thing)
      else
        re_compute(thing)
      end
    end
  end
  
  # good
  def compute_thing(thing)
    return unless thing[:foo]
    update_with_bar(thing[:foo])
    return re_compute(thing) unless thing[:foo][:bar]
    partial_compute(thing)
  end

  Prefer next in loops instead of conditional blocks.

  # bad
  [0, 1, 2, 3].each do |item|
    if item > 1
      puts item
    end
  end
  
  # good
  [0, 1, 2, 3].each do |item|
    next unless item > 1
    puts item
  end

• Prefer map over collect, find over detect, select over find_all, reduce over inject and size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use of select is encouraged over find_all is that it goes together nicely with reject and its name is pretty self-explanatory. 哈哈哈，我就说 Ruby 这些关键词……map 比 collect 好。:hearts:

• Don't use count as a substitute for size. For Enumerable objects other than Array it will iterate the entire collection in order to determine its size.

  # bad
  some_hash.count
  
  # good
  some_hash.size

• Use flat_map instead of map + flatten. This does not apply for arrays with a depth greater than 2, i.e. if users.first.songs == ['a', ['b','c']], then use map + flatten rather than flat_map. flat_map flattens the array by 1, whereas flatten flattens it all the way. 好像很有用的样子。

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

• Prefer reverse_each to reverse.each because some classes that include Enumerable will provide an efficient implementation. Even in the worst case where a class does not provide a specialized implementation, the general implementation inherited from Enumerable will be at least as efficient as using reverse.each. 这个……其实是说不要生成不必要的拷贝，能直接反着用 iterator，干嘛要把整个数组都反过来， 再 each 啊！

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

Naming

The only real difficulties in programming are cache invalidation and naming things.

-- Phil Karlton

• Name identifiers in English. 哈哈哈，Ruby 还可以用中文的。

  # 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

• Use snake_case for symbols, methods and variables. 和 C 语言变量的风格一样。

  # bad
  :'some symbol'
  :SomeSymbol
  :someSymbol
  
  someVar = 5
  var_10  = 10
  
  def someMethod
    # some code
  end
  
  def SomeMethod
    # some code
  end
  
  # good
  :some_symbol
  
  some_var = 5
  var10    = 10
  
  def some_method
    # some code
  end

• Do not separate numbers from letters on symbols, methods and variables. 这个规则有点细致。不要把数字单独分出来。我觉得这个还要看情况把。

  # bad
  :some_sym_1
  
  some_var_1 = 1
  
  def some_method_1
    # some code
  end
  
  # good
  :some_sym1
  
  some_var1 = 1
  
  def some_method1
    # some code
  end

• Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.) 这个和 C++ 类似。 这里有一点，专有名词比如 HTTP 本来就大写，就不要弄成 HttpClient 了。

  # bad
  class Someclass
    # some code
  end
  
  class Some_Class
    # some code
  end
  
  class SomeXml
    # some code
  end
  
  class XmlSomething
    # some code
  end
  
  # good
  class SomeClass
    # some code
  end
  
  class SomeXML
    # some code
  end
  
  class XMLSomething
    # some code
  end

• Use snake_case for naming files, e.g. hello_world.rb. 文件名，用下划线分隔。（我似乎更喜欢用 dash，hyphen。）

  Use snake_case for naming directories, e.g. lib/hello_world/hello_world.rb.

  Aim to have just a single class/module per source file. Name the file name as the class/module, but replacing CamelCase with snake_case.

• Use SCREAMING_SNAKE_CASE for other constants.

  # bad
  SomeConst = 5
  
  # good
  SOME_CONST = 5

  这个 STDOUT 不也是么。

• The names of predicate methods (methods that return a boolean value) should end in a question mark. (i.e. Array#empty?). Methods that don't return a boolean, shouldn't end in a question mark.

  predict 谓词，这个 method 后面加上 ?，更清晰。

• Avoid prefixing predicate methods with the auxiliary verbs such as is, does, or can. These words are redundant and inconsistent with the style of boolean methods in the Ruby core library, such as empty? and include?. 既然后面有了 ？，前面就不要什么“is_”，“has_” 啥的了。

  # bad
  class Person
    def is_tall?
      true
    end
  
    def can_play_basketball?
      false
    end
  
    def does_like_candy?
      true
    end
  end
  
  # good
  class Person
    def tall?
      true
    end
  
    def basketball_player?
      false
    end
  
    def likes_candy?
      true
    end
  end

• The names of potentially dangerous methods (i.e. methods that modify self or the arguments, exit! (doesn't run the finalizers like exit does), etc.) should end with an exclamation mark if there exists a safe version of that dangerous method. 如果有两个版本，一个不安全的 inplace，一个安全的，不安全的那个后面加上“！”。 这个其实……还好啦。是个人都会这么写得。

  # bad - there is no 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

• Define the non-bang (safe) method in terms of the bang (dangerous) one if possible. 能搞一个非 intrusive 的安全的 non-bang 的 method，就整一个。

  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

• When defining binary operators, name the parameter other(<< and [] are exceptions to the rule, since their semantics are different). 这个……就是说定义二元操作符的时候，参数要用 other……这个也太细致了。 当然这个单词推荐得还不错。

  def +(other)
    # body omitted
  end

Comments

Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?" Improve the code and then document it to make it even clearer.

-- Steve McConnell

• Write self-documenting code and ignore the rest of this section. Seriously! 代码写得好，注释都可以不要。

• Write comments in English. 中文注释要不得！（不要学我做笔记用中文）

  外，扯个淡，我之所以用中文做代码笔记，是因为中文和英文有天然的隔离性， 很容易从视觉上区分。这样我就能快速地看到自己的笔记，而不是傻傻找半天， 不知道自己地笔记在哪。

• Use one space between the leading # character of the comment and the text of the comment.

• Comments longer than a word are capitalized and use punctuation. Use one space after periods. 哈哈，这是作者吐槽，如果注释超过一个单词，特么这就是要给英文句子， 要遵守英文文法。标点符号要用对啊！

• Avoid superfluous comments. 这种注释写来干嘛啊……把代码翻译一遍，不叫注释。（当然，如果你不懂这个用法， 这就是笔记，而不是注释，是可以接受的。（我经常干这样的事。））

  # bad
  counter += 1 # Increments counter by one.

• Keep existing comments up-to-date. An outdated comment is worse than no comment at all. 这个其实……当然，不要代码改了注释不更新，反而误导看客。

Good code is like a good joke: it needs no explanation. — old programmers maxim, through Russ Olsen

• Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory. ("Do or do not—there is no try." Yoda)

Comment Annotations

• Annotations should usually be written on the line immediately above the relevant code.

• The annotation keyword is followed by a colon and a space, then a note describing the problem.

• If multiple lines are required to describe the problem, subsequent lines should be indented three spaces after the # (one general plus two for indentation purpose). 这个太对了！我都是这样的！4 总是一个不错地 indent 尺度。

  def bar
    # FIXME: This has crashed occasionally since v3.2.1. It may
    #   be related to the BarBazUtil upgrade.
    baz(:quux)
  end

• In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

  def bar
    sleep 100 # OPTIMIZE
  end

• TODO, OPTIMIZE, REVIEW, FIXME, 这些常用的标签，用起来。用对。

  Use TODO to note missing features or functionality that should be added at a later date.

  Use FIXME to note broken code that needs to be fixed.

  Use OPTIMIZE to note slow or inefficient code that may cause performance problems.

  Use HACK to note code smells where questionable coding practices were used and should be refactored away.

  Use REVIEW to note anything that should be looked at to confirm it is working as intended. For example: REVIEW: Are we sure this is how the client does X currently?

  Use other custom annotation keywords if it feels appropriate, but be sure to document them in your project's README or similar.

Magic Comments

• Place magic comments above all code and documentation. Magic comments should only go below shebangs if they are needed in your source file.

  magic comments 有点像配置说明啥的。如果对一个 Class 进行整体地功能性描述。 按照英文文法排版。

  # good
  # frozen_string_literal: true
  # Some documentation about Person
  class Person
  end
  
  # bad
  # Some documentation about Person
  # frozen_string_literal: true
  class Person
  end

  # good
  #!/usr/bin/env ruby
  # frozen_string_literal: true
  App.parse(ARGV)
  
  # bad
  # frozen_string_literal: true
  #!/usr/bin/env ruby
  App.parse(ARGV)

• Use one magic comment per line if you need multiple.

  # good
  # frozen_string_literal: true
  # encoding: ascii-8bit
  
  # bad
  # -*- frozen_string_literal: true; encoding: ascii-8bit -*-

• Separate magic comments from code and documentation with a blank line.

  # good
  # frozen_string_literal: true
  
  # Some documentation for Person
  class Person
    # Some code
  end
  
  # bad
  # frozen_string_literal: true
  # Some documentation for Person
  class Person
    # Some code
  end

  哦……好吧。

Classes & Modules

• Use a consistent structure in your class definitions. 自己要守自己的规矩啊！（守规矩是节约体力的事，因为你不要思考下次怎么弄，“按照规矩！”就好。）

  class Person
    # extend and include go first
    extend SomeModule
    include AnotherModule
  
    # inner classes
    CustomError = Class.new(StandardError)
  
    # constants are next
    SOME_CONSTANT = 20
  
    # afterwards we have attribute macros
    attr_reader :name
  
    # followed by other macros (if any)
    validates :name
  
    # public class methods are next in line
    def self.some_method
    end
  
    # initialization goes between class methods and other instance methods
    def initialize
    end
  
    # followed by other public instance methods
    def some_method
    end
  
    # protected and private methods are grouped near the end
    protected
  
    def some_protected_method
    end
  
    private
  
    def some_private_method
    end
  end

• Split multiple mixins into separate statements. 如何引入别的代码？mixins 是这个意思啊……

  # bad
  class Person
    include Foo, Bar
  end
  
  # good
  class Person
    # multiple mixins go in separate statements
    include Foo
    include Bar
  end

• Don't nest multi-line classes within classes. Try to have such nested classes each in their own file in a folder named like the containing class. 这个其实说的是文件结构或者代码组织。

  # bad
  
  # foo.rb
  class Foo
    class Bar
      # 30 methods inside
    end
  
    class Car
      # 20 methods inside
    end
  
    # 30 methods inside
  end
  
  # good
  
  # foo.rb
  class Foo
    # 30 methods inside
  end
  
  # foo/bar.rb
  class Foo
    class Bar
      # 30 methods inside
    end
  end
  
  # foo/car.rb
  class Foo
    class Car
      # 20 methods inside
    end
  end

• Prefer modules to classes with only class methods. Classes should be used only when it makes sense to create instances out of them. 这个是程序逻辑上的东西，和 Ruby 无关。Modules 是一些 functions， Class 是面向对象的一些东西。

  # bad
  class SomeClass
    def self.some_method
      # body omitted
    end
  
    def self.some_other_method
      # body omitted
    end
  end
  
  # good
  module SomeModule
    module_function
  
    def some_method
      # body omitted
    end
  
    def some_other_method
      # body omitted
    end
  end

• Favor the use of module_function over extend self when you want to turn a module's instance methods into class methods.

  # bad
  module Utilities
    extend self
  
    def parse_something(string)
      # do stuff here
    end
  
    def other_utility_method(number, string)
      # do some more stuff
    end
  end
  
  # good
  module Utilities
    module_function
  
    def parse_something(string)
      # do stuff here
    end
  
    def other_utility_method(number, string)
      # do some more stuff
    end
  end

• When designing class hierarchies make sure that they conform to the Liskov Substitution Principle.

• Try to make your classes as SOLID as possible.

• Always supply a proper to_s method for classes that represent domain objects. 记得定义一个 to_s 方法。

  class Person
    attr_reader :first_name, :last_name
  
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  
    def to_s
      "#{@first_name} #{@last_name}"
    end
  end

• Use the attr family of functions to define trivial accessors or mutators. 这特么不是 Ruby 风格，这是 Ruby 经验谈了。

  # bad
  class Person
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  
    def first_name
      @first_name
    end
  
    def last_name
      @last_name
    end
  end
  
  # good
  class Person
    attr_reader :first_name, :last_name
  
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  end

• For accessors and mutators, avoid prefixing method names with get_ and set_. It is a Ruby convention to use attribute names for accessors (readers) and attr_name= for mutators (writers).

  # bad
  class Person
    def get_name
      "#{@first_name} #{@last_name}"
    end
  
    def set_name(name)
      @first_name, @last_name = name.split(' ')
    end
  end
  
  # good
  class Person
    def name
      "#{@first_name} #{@last_name}"
    end
  
    def name=(name)
      @first_name, @last_name = name.split(' ')
    end
  end

• Avoid the use of attr. Use attr_reader and attr_accessor instead. 不用 attr（这个语法太蛋疼了），用 attr_reader、attr_writer 和 attr_accessor。

  # bad - creates a single attribute accessor (deprecated in Ruby 1.9)
  attr :something, true
  attr :one, :two, :three # behaves as attr_reader
  
  # good
  attr_accessor :something
  attr_reader :one, :two, :three

• Consider using Struct.new, which defines the trivial accessors, constructor and comparison operators for you. 如果只是一些变量的 get/set，用 Struct.new 似乎更简洁。

  # good
  class Person
    attr_accessor :first_name, :last_name
  
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  end
  
  # better
  Person = Struct.new(:first_name, :last_name) do
  end

• Don't extend an instance initialized by Struct.new. Extending it introduces a superfluous class level and may also introduce weird errors if the file is required multiple times.

  # bad
  class Person < Struct.new(:first_name, :last_name)
  end
  
  # good
  Person = Struct.new(:first_name, :last_name)

• Consider adding factory methods to provide additional sensible ways to create instances of a particular class.

  class Person
    def self.create(options_hash)
      # body omitted
    end
  end

• Prefer duck-typing over inheritance. 其实就是说不要掉 oop 的书袋，用 duck-tpying，表现层符合预期就好。不要死活 往继承上套。

  # bad
  class Animal
    # abstract method
    def speak
    end
  end
  
  # extend superclass
  class Duck < Animal
    def speak
      puts 'Quack! Quack'
    end
  end
  
  # extend superclass
  class Dog < Animal
    def speak
      puts 'Bau! Bau!'
    end
  end
  
  # good
  class Duck
    def speak
      puts 'Quack! Quack'
    end
  end
  
  class Dog
    def speak
      puts 'Bau! Bau!'
    end
  end

• Avoid the usage of class (@@) variables due to their "nasty" behavior in inheritance. 这个有点蛋疼啊……是共享了的 refenrece 嘛？

  class Parent
    @@class_var = 'parent'
  
    def self.print_class_var
      puts @@class_var
    end
  end
  
  class Child < Parent
    @@class_var = 'child'
  end
  
  Parent.print_class_var # => will print 'child'

  As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.

• Assign proper visibility levels to methods (private, protected) in accordance with their intended usage. Don't go off leaving everything public (which is the default). After all we're coding in Ruby now, not in Python. 这个 Ruby 啊……默认是 public 的，所以不要搞一堆画蛇添足的东西……

• Indent the public, protected, and private methods as much as the method definitions they apply to. Leave one blank line above the visibility modifier and one blank line below in order to emphasize that it applies to all methods below it. 分隔开……这个和 C++ 类似了。

  class SomeClass
    def public_method
      # some code
    end
  
    private
  
    def private_method
      # some code
    end
  
    def another_private_method
      # some code
    end
  end

• Use def self.method to define class methods. This makes the code easier to refactor since the class name is not repeated. 定义 self.method，是 class method。

  class TestClass
    # bad
    def TestClass.some_method
      # body omitted
    end
  
    # good
    def self.some_other_method
      # body omitted
    end
  
    # Also possible and convenient when you
    # have to define many class methods.
    class << self
      def first_method
        # body omitted
      end
  
      def second_method_etc
        # body omitted
      end
    end
  end

• Prefer alias when aliasing methods in lexical class scope as the resolution of self in this context is also lexical, and it communicates clearly to the user that the indirection of your alias will not be altered at runtime or by any subclass unless made explicit.

  class Westerner
    def first_name
      @names.first
    end
  
    alias given_name first_name
  end

  Since alias, like def, is a keyword, prefer bareword arguments over symbols or strings. In other words, do alias foo bar, not alias :foo :bar.

  Also be aware of how Ruby handles aliases and inheritance: an alias references the method that was resolved at the time the alias was defined; it is not dispatched dynamically.

  class Fugitive < Westerner
    def first_name
      'Nobody'
    end
  end

  In this example, Fugitive#given_name would still call the original Westerner#first_name method, not Fugitive#first_name. To override the behavior of Fugitive#given_name as well, you'd have to redefine it in the derived class.

  class Fugitive < Westerner
    def first_name
      'Nobody'
    end
  
    alias given_name first_name
  end

• Always use alias_method when aliasing methods of modules, classes, or singleton classes at runtime, as the lexical scope of alias leads to unpredictability in these cases.

  module Mononymous
    def self.included(other)
      other.class_eval { alias_method :full_name, :given_name }
    end
  end
  
  class Sting < Westerner
    include Mononymous
  end

• When class (or module) methods call other such methods, omit the use of a leading self or own name followed by a . when calling other such methods. This is often seen in "service classes" or other similar concepts where a class is treated as though it were a function. This convention tends to reduce repetitive boilerplate in such classes. 定义 class 或者 module methods 的时候要加上 self，但是互相调用的时候，不用 加 self。

  class TestClass
    # bad -- more work when class renamed/method moved
    def self.call(param1, param2)
      TestClass.new(param1).call(param2)
    end
  
    # bad -- more verbose than necessary
    def self.call(param1, param2)
      self.new(param1).call(param2)
    end
  
    # good
    def self.call(param1, param2)
      new(param1).call(param2)
    end
  
    # ...other methods...
  end

Exceptions

• Prefer raise over fail for exceptions. raise 比 fail 好。

  # bad
  fail SomeException, 'message'
  
  # good
  raise SomeException, 'message'

• Don't specify RuntimeError explicitly in the two argument version of raise. 直接 raise 就好，不用加上 RuntimeError。

  # bad
  raise RuntimeError, 'message'
  
  # good - signals a RuntimeError by default
  raise 'message'

• Prefer supplying an exception class and a message as two separate arguments to raise, instead of an exception instance. 在你 raise exception 的时候，不要用 new……直接用两个参数就好。

  # bad
  raise SomeException.new('message')
  # Note that there is no way to do `raise SomeException.new('message'), backtrace`.
  
  # good
  raise SomeException, 'message'
  # Consistent with `raise SomeException, 'message', backtrace`.

• Do not return from an ensure block. If you explicitly return from a method inside an ensure block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised at all. In effect, the exception will be silently thrown away. 这个很有意思，如果你在 enusre 里面 return，raise 的东西就不见了。好像没有 raise error 一样。

  # bad
  def foo
    raise
  ensure
    return 'very bad idea'
  end

• Use implicit begin blocks where possible. 总之不要多余的东西。能精炼就精炼。

  # bad
  def foo
    begin
      # main logic goes here
    rescue
      # failure handling goes here
    end
  end
  
  # good
  def foo
    # main logic goes here
  rescue
    # failure handling goes here
  end

• Mitigate the proliferation of begin blocks by using contingency methods (a term coined by Avdi Grimm).

  proliferation
      [pro,lɪfə'reʃən; prəʊ,lɪfə'reɪʃn]
      n. 增殖，扩散；分芽繁殖
  
  contingency
      英 [kən'tɪndʒ(ə)nsɪ] 美 [kən'tɪndʒənsi]
      n. 偶然性；[安全] 意外事故；可能性；[审计] 意外开支；[离散数学或逻辑学]偶然式
  

  # bad
  begin
    something_that_might_fail
  rescue IOError
    # handle IOError
  end
  
  begin
    something_else_that_might_fail
  rescue IOError
    # handle IOError
  end
  
  # good
  def with_io_error_handling
     yield
  rescue IOError
    # handle IOError
  end
  
  with_io_error_handling { something_that_might_fail }
  with_io_error_handling { something_else_that_might_fail }

• Don't suppress exceptions. 看了这个……我学到的是如何 supress exceptions……

  # bad
  begin
    # an exception occurs here
  rescue SomeError
    # the rescue clause does absolutely nothing
  end
  
  # bad
  do_something rescue nil

• Avoid using rescue in its modifier form. 不要用 modifier 的 rescue（后置的）。咋说呢， 你最好一个一个 rescue……（好累的赶脚）

  # bad - this catches exceptions of StandardError class and its descendant classes
  read_file rescue handle_error($!)
  
  # good - this catches only the exceptions of Errno::ENOENT class and its descendant classes
  def foo
    read_file
  rescue Errno::ENOENT => ex
    handle_error(ex)
  end

• Don't use exceptions for flow of control. 其实……这是在权衡啥样的是程序应该处理的，啥样的是输入有问题，应当从输入上消弭的。

  # bad
  begin
    n / d
  rescue ZeroDivisionError
    puts 'Cannot divide by 0!'
  end
  
  # good
  if d.zero?
    puts 'Cannot divide by 0!'
  else
    n / d
  end

• Avoid rescuing the Exception class. This will trap signals and calls to exit, requiring you to kill -9 the process.

  # bad
  begin
    # calls to exit and kill signals will be caught (except kill -9)
    exit
  rescue Exception
    puts "you didn't really want to exit, right?"
    # exception handling
  end
  
  # good
  begin
    # a blind rescue rescues from StandardError, not Exception as many
    # programmers assume.
  rescue => e
    # exception handling
  end
  
  # also good
  begin
    # an exception occurs here
  rescue StandardError => e
    # exception handling
  end

• Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from. 这个和 Ruby 也无关啊……rescue 是不断 fall back，当然要把最后的“default”放后面咯。

  # bad
  begin
    # some code
  rescue StandardError => e
    # some handling
  rescue IOError => e
    # some handling that will never be executed
  end
  
  # good
  begin
    # some code
  rescue IOError => e
    # some handling
  rescue StandardError => e
    # some handling
  end

• Release external resources obtained by your program in an ensure block. 这时，应当怀念 Java 的 try with resources 语法……

  f = File.open('testfile')
  begin
    # .. process
  rescue
    # .. handle error
  ensure
    f.close if f
  end

• Use versions of resource obtaining methods that do automatic resource cleanup when possible. 有自动的，好用的，特么干嘛自己造稀烂的轮子啊！

  # bad - you need to close the file descriptor explicitly
  f = File.open('testfile')
  # some action on the file
  f.close
  
  # good - the file descriptor is closed automatically
  File.open('testfile') do |f|
    # some action on the file
  end

• Favor the use of exceptions from the standard library over introducing new exception classes.

Collections

• Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is). 跟 JavaScript 一样，能用 var list = [] 干嘛用那个恶心的构造函数语法啊！

  # bad
  arr = Array.new
  hash = Hash.new
  
  # good
  arr = []
  arr = Array.new(10)
  hash = {}
  hash = Hash.new(0)

• Prefer %w to the literal array syntax when you need an array of words (non-empty strings without spaces and special characters in them). Apply this rule only to arrays with two or more elements. 这个其实也是见仁见智的……后者显然更清晰。 从别的地方拷贝来一串路径啥的，用这样的语法也能直接用，不必放到 Vim 里面修改。

  # bad
  STATES = ['draft', 'open', 'closed']
  
  # good
  STATES = %w[draft open closed]

• Prefer %i to the literal array syntax when you need an array of symbols (and you don't need to maintain Ruby 1.9 compatibility). Apply this rule only to arrays with two or more elements. 这是 symbol 的快速构造。

  # bad
  STATES = [:draft, :open, :closed]
  
  # good
  STATES = %i[draft open closed]

• Avoid comma after the last item of an Array or Hash literal, especially when the items are not on separate lines. 这个上面说过……其实我还挺喜欢的……

  # 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]

• Avoid the creation of huge gaps in arrays. 这个是程序设计上的问题。干嘛不用 Hash 呢？

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

• When accessing the first or last element from an array, prefer first or last over [0] or [-1]. 蛤……这个……还好吧。first，last 确实好用。但是 [0] 和 [-1] 好记啊！

• Use Set instead of Array when dealing with unique elements. Set implements a collection of unordered values with no duplicates. This is a hybrid of Array's intuitive inter-operation facilities and Hash's fast lookup. 这个是数据结构的选择，和 Ruby 也没啥关系。

• Prefer symbols instead of strings as hash keys. 我想知道这两个 hash 是一样的嘛？

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

• Avoid the use of mutable objects as hash keys. 这个……是 hash 的特性，如果 key 变了，它的 entry 就应当变， 这个和 hash 冲突。

• Use the Ruby 1.9 hash literal syntax when your hash keys are symbols. 似乎是不一样的。不过这个语法看上去和 JS 一样了。

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

• Don't mix the Ruby 1.9 hash syntax with hash rockets in the same hash literal. When you've got keys that are not symbols stick to the hash rockets syntax. 这个符号又叫 rocket syntax 了啊……？！有人叫它 fat arrow……

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

• Use Hash#key? instead of Hash#has_key? and Hash#value? instead of Hash#has_value?. 有“？”号就不要画蛇添足啦。

  # bad
  hash.has_key?(:test)
  hash.has_value?(value)
  
  # good
  hash.key?(:test)
  hash.value?(value)

• Use Hash#each_key instead of Hash#keys.each and Hash#each_value instead of Hash#values.each. each_key 和 each_value 估计效率好点。

  # bad
  hash.keys.each { |k| p k }
  hash.values.each { |v| p v }
  hash.each { |k, _v| p k }
  hash.each { |_k, v| p v }
  
  # good
  hash.each_key { |k| p k }
  hash.each_value { |v| p v }

• Use Hash#fetch when dealing with hash keys that should be present. 接送函数不错。== fetch。还可以设定默认值。

  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)

  Introduce default values for hash keys via Hash#fetch as opposed to using custom logic.

  batman = { name: 'Bruce Wayne', is_evil: false }
  
  # bad - if we just use || operator with falsy value we won't get the expected result
  # 所以这特么还是错的……所以这根本不叫风格！这叫误用。
  batman[:is_evil] || true # => true
  
  # good - fetch work correctly with falsy values
  batman.fetch(:is_evil, true) # => false

• Prefer the use of the block instead of the default value in Hash#fetch if the code that has to be evaluated may have side effects or be expensive. 这个……蛤？

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

• Use Hash#values_at when you need to retrieve several values consecutively from a hash. 一次取出好几个，就用 values_at……

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

• Rely on the fact that as of Ruby 1.9 hashes are ordered. 蛤，hash 都是 ordered_hash……==Java 反正是提供了好几种 Hash。

• Do not modify a collection while traversing it. 这是数据结构上的建议。

• When accessing elements of a collection, avoid direct access via [n] by using an alternate form of the reader method if it is supplied. This guards you from calling [] on nil. 哈哈哈哈好吧。原来这样更好。

  # bad
  Regexp.last_match[1]
  
  # good
  Regexp.last_match(1)

• When providing an accessor for a collection, provide an alternate form to save users from checking for nil before accessing an element in the collection. 用默认值设定为 nil 来避免过多的无畏判断。

  # bad
  def awesome_things
    @awesome_things
  end
  
  # good
  def awesome_things(index = nil)
    if index && @awesome_things
      @awesome_things[index]
    else
      @awesome_things
    end
  end

Numbers

• Use Integer check type of an integer number. Since Fixnum is platform-dependent, checking against it will return different results on 32-bit and 64-bit machines.

  timestamp = Time.now.to_i
  
  # bad
  timestamp.is_a? Fixnum
  timestamp.is_a? Bignum
  
  # good
  timestamp.is_a? Integer

• Prefer to use ranges when generating random numbers instead of integers with offsets, since it clearly states your intentions. Imagine simulating a role of a dice: 还可以这样 rand……

  # bad
  rand(6) + 1
  
  # good
  rand(1..6)

Strings

• Prefer string interpolation and string formatting instead of string concatenation: 字符串拼接总是效率差，而且难看。

  # bad
  email_with_name = user.name + ' <' + user.email + '>'
  
  # good
  email_with_name = "#{user.name} <#{user.email}>"
  
  # good
  email_with_name = format('%s <%s>', user.name, user.email)

• Adopt a consistent string literal quoting style. There are two popular styles in the Ruby community, both of which are considered good—single quotes by default (Option A) and double quotes by default (Option B). 如果不需要 escape char，也没有 string interpolation 的话……就用单引号。

  • (Option A) Prefer single-quoted strings when you don't need string interpolation or special symbols such as \t, \n, ', etc.

    # bad
    name = "Bozhidar"
    
    # good
    name = 'Bozhidar'

  • (Option B) Prefer double-quotes unless your string literal contains " or escape characters you want to suppress.

    # bad
    name = 'Bozhidar'
    
    # good
    name = "Bozhidar"

  The string literals in this guide are aligned with the first style.

• Don't use the character literal syntax ?x. Since Ruby 1.9 it's basically redundant—?x would interpreted as 'x' (a string with a single character in it). 哦……看得书老，还觉得这样好呢……

  # bad
  char = ?c
  
  # good
  char = 'c'

• Don't leave out {} around instance and global variables being interpolated into a string. 这特么上面说过了……

  class Person
    attr_reader :first_name, :last_name
  
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  
    # bad - valid, but awkward
    def to_s
      "#@first_name #@last_name"
    end
  
    # good
    def to_s
      "#{@first_name} #{@last_name}"
    end
  end
  
  $global = 0
  # bad
  puts "$global = #$global"
  
  # good
  puts "$global = #{$global}"

• Don't use Object#to_s on interpolated objects. It's invoked on them automatically. 同样，不要画蛇添足，这个自动 implicitely 转化的……

  # bad
  message = "This is the #{result.to_s}."
  
  # good
  message = "This is the #{result}."

• Avoid using String#+ when you need to construct large data chunks. Instead, use String#<<. Concatenation mutates the string instance in-place and is always faster than String#+, which creates a bunch of new string objects. 即使要 string concat，也要用 String#<< 函数。

  # bad
  html = ''
  html += '<h1>Page title</h1>'
  
  paragraphs.each do |paragraph|
    html += "<p>#{paragraph}</p>"
  end
  
  # good and also fast
  html = ''
  html << '<h1>Page title</h1>'
  
  paragraphs.each do |paragraph|
    html << "<p>#{paragraph}</p>"
  end

• Don't use String#gsub in scenarios in which you can use a faster more specialized alternative.

  url = 'http://example.com'
  str = 'lisp-case-rules'
  
  # bad
  url.gsub('http://', 'https://')
  str.gsub('-', '_')
  
  # good
  url.sub('http://', 'https://')
  str.tr('-', '_')

• When using heredocs for multi-line strings keep in mind the fact that they preserve leading whitespace. It's a good practice to employ some margin based on which to trim the excessive whitespace. 这个酷毙了……不过……好像有点效率问题。

  code = <<-END.gsub(/^\s+\|/, '')
    |def test
    |  some_method
    |  other_method
    |end
  END
  # => "def test\n  some_method\n  other_method\nend\n"

• Use Ruby 2.3's squiggly heredocs for nicely indented multi-line strings.

  # bad - using Powerpack String#strip_margin
  code = <<-END.strip_margin('|')
    |def test
    |  some_method
    |  other_method
    |end
  END
  
  # also bad
  code = <<-END
  def test
    some_method
    other_method
  end
  END
  
  # good
  code = <<~END
    def test
      some_method
      other_method
    end
  END

Date & Time

• Prefer Time.now over Time.new when retrieving the current system time.

• Don't use DateTime unless you need to account for historical calendar reform -- and if you do, explicitly specify the start argument to clearly state your intentions. :hearts:

  # bad - uses DateTime for current time
  DateTime.now
  
  # good - uses Time for current time
  Time.now
  
  # bad - uses DateTime for modern date
  DateTime.iso8601('2016-06-29')
  
  # good - uses Date for modern date
  Date.iso8601('2016-06-29')
  
  # good - uses DateTime with start argument for historical date
  DateTime.iso8601('1751-04-23', Date::ENGLAND)

Regular Expressions

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.

-- Jamie Zawinski

• Don't use regular expressions if you just need plain text search in string: string['text']

• For simple constructions you can use regexp directly through string index.

  match = string[/regexp/]             # get content of matched regexp
  first_group = string[/text(grp)/, 1] # get content of captured group
  string[/text (grp)/, 1] = 'replace'  # string => 'text replace'

• Use non-capturing groups when you don't use the captured result.

  # bad
  /(first|second)/
  
  # good
  /(?:first|second)/

• Don't use the cryptic Perl-legacy variables denoting last regexp group matches ($1, $2, etc). Use Regexp.last_match(n) instead. 哈哈，Ruby 也有这样的东西啊！

  /(regexp)/ =~ string
  ...
  
  # bad
  process $1
  
  # good
  process Regexp.last_match(1)

• Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead. 当然要用 named captutre 啊！

  # bad
  /(regexp)/ =~ string
  # some code
  process Regexp.last_match(1)
  
  # good
  /(?<meaningful_var>regexp)/ =~ string
  # some code
  process meaningful_var

• Character classes have only a few special characters you should care about: ^, -, \, ], so don't escape . or brackets in [].

• Be careful with ^ and $ as they match start/end of line, not string endings. If you want to match the whole string use: \A and \z (not to be confused with \Z which is the equivalent of /\n?\z/).

  string = "some injection\nusername"
  string[/^username$/]   # matches
  string[/\Ausername\z/] # doesn't match

• Use x modifier for complex regexps. This makes them more readable and you can add some useful comments. Just be careful as spaces are ignored. 这个 Perl 也有的。

  regexp = /
    start         # some text
    \s            # white space char
    (group)       # first group
    (?:alt1|alt2) # some alternation
    end
  /x

• For complex replacements sub/gsub can be used with a block or a hash.

  words = 'foo bar'
  words.sub(/f/, 'f' => 'F') # => 'Foo bar'
  words.gsub(/\w+/) { |word| word.capitalize } # => 'Foo Bar'

Percent Literals

• Use %()(it's a shorthand for %Q) for single-line strings which require both interpolation and embedded double-quotes. For multi-line strings, prefer heredocs.

  # bad (no interpolation needed)
  %(<div class="text">Some text</div>)
  # should be '<div class="text">Some text</div>'
  
  # bad (no double-quotes)
  %(This is #{quality} style)
  # should be "This is #{quality} style"
  
  # bad (multiple lines)
  %(<div>\n<span class="big">#{exclamation}</span>\n</div>)
  # should be a heredoc.
  
  # good (requires interpolation, has quotes, single line)
  %(<tr><td class="name">#{name}</td>)

• Avoid %() or the equivalent %q() unless you have a string with both ' and " in it. Regular string literals are more readable and should be preferred unless a lot of characters would have to be escaped in them.

  # bad
  name = %q(Bruce Wayne)
  time = %q(8 o'clock)
  question = %q("What did you say?")
  
  # good
  name = 'Bruce Wayne'
  time = "8 o'clock"
  question = '"What did you say?"'
  quote = %q(<p class='quote'>"What did you say?"</p>)

• Use %r only for regular expressions matching at least one '/' character.

  # bad
  %r{\s+}
  
  # good
  %r{^/(.*)$}
  %r{^/blog/2011/(.*)$}

• Avoid the use of %x unless you're going to invoke a command with backquotes in it(which is rather unlikely).

  # bad
  date = %x(date)
  
  # good
  date = `date`
  echo = %x(echo `date`)

• Avoid the use of %s. It seems that the community has decided :"some string" is the preferred way to create a symbol with spaces in it. 好吧……因为手写确实也不麻烦。

• Use the braces that are the most appropriate for the various kinds of percent literals. 这个……也有倾向性哈哈。

  • () for string literals(%q, %Q).
  • [] for array literals(%w, %i, %W, %I) as it is aligned with the standard array literals.
  • {} for regexp literals(%r) since parentheses often appear inside regular expressions. That's why a less common character with { is usually the best delimiter for %r literals.
  • () for all other literals (e.g. %s, %x)

  # bad
  %q{"Test's king!", John said.}
  
  # good
  %q("Test's king!", John said.)
  
  # bad
  %w(one two three)
  %i(one two three)
  
  # good，确实看上去好点
  %w[one two three]
  %i[one two three]
  
  # bad
  %r((\w+)-(\d+))
  %r{\w{1,2}\d{2,5}}
  
  # good
  %r{(\w+)-(\d+)}
  %r|\w{1,2}\d{2,5}|

Metaprogramming

（这部分我似乎看不懂啊……）

• Avoid needless metaprogramming. 当头一棒……（叫你炫技……）

• Do not mess around in core classes when writing libraries. (Do not monkey-patch them.)

• The block form of class_eval is preferable to the string-interpolated form.

  when you use the string-interpolated form, always supply __FILE__ and __LINE__, so that your backtraces make sense:

  class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__

• define_method is preferable to class_eval{ def ... }

• When using class_eval (or other eval) with string interpolation, add a comment block showing its appearance if interpolated (a practice used in Rails code):

  # from activesupport/lib/active_support/core_ext/string/output_safety.rb
  UNSAFE_STRING_METHODS.each do |unsafe_method|
    if 'String'.respond_to?(unsafe_method)
      class_eval <<-EOT, __FILE__, __LINE__ + 1
        def #{unsafe_method}(*params, &block)       # def capitalize(*params, &block)
          to_str.#{unsafe_method}(*params, &block)  #   to_str.capitalize(*params, &block)
        end                                       # end
  
        def #{unsafe_method}!(*params)              # def capitalize!(*params)
          @dirty = true                           #   @dirty = true
          super                                   #   super
        end                                       # end
      EOT
    end
  end

• Avoid using method_missing for metaprogramming because backtraces become messy, the behavior is not listed in #methods, and misspelled method calls might silently work, e.g. nukes.launch_state = false. Consider using delegation, proxy, or define_method instead. If you must use method_missing:

• Be sure to also define respond_to_missing?

• Only catch methods with a well-defined prefix, such as find_by_* -- make your code as assertive as possible.

• Call super at the end of your statement

• Delegate to assertive, non-magical methods:

  # bad
  def method_missing?(meth, *params, &block)
    if /^find_by_(?<prop>.*)/ =~ meth
      # ... lots of code to do a find_by
    else
      super
    end
  end
  
  # good
  def method_missing?(meth, *params, &block)
    if /^find_by_(?<prop>.*)/ =~ meth
      find_by(prop, *params, &block)
    else
      super
    end
  end
  
  # best of all, though, would to define_method as each findable attribute is declared

• Prefer public_send over send so as not to circumvent private/protected visibility.

  # We have  an ActiveModel Organization that includes concern Activatable
  module Activatable
    extend ActiveSupport::Concern
  
    included do
      before_create :create_token
    end
  
    private
  
    def reset_token
      # some code
    end
  
    def create_token
      # some code
    end
  
    def activate!
      # some code
    end
  end
  
  class Organization < ActiveRecord::Base
    include Activatable
  end
  
  linux_organization = Organization.find(...)
  # BAD - violates privacy
  linux_organization.send(:reset_token)
  # GOOD - should throw an exception
  linux_organization.public_send(:reset_token)

• Prefer __send__ over send, as send may overlap with existing methods.

  require 'socket'
  
  u1 = UDPSocket.new
  u1.bind('127.0.0.1', 4913)
  u2 = UDPSocket.new
  u2.connect('127.0.0.1', 4913)
  # Won't send a message to the receiver obj.
  # Instead it will send a message via UDP socket.
  u2.send :sleep, 0
  # Will actually send a message to the receiver obj.
  u2.__send__ ...

Misc

• Write ruby -w safe code.

• Avoid hashes as optional parameters. Does the method do too much? (Object initializers are exceptions for this rule).

• Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC.

• Avoid parameter lists longer than three or four parameters.

• If you really need "global" methods, add them to Kernel and make them private.

• Use module instance variables instead of global variables.

  # bad
  $foo_bar = 1
  
  # good
  module Foo
    class << self
      attr_accessor :bar
    end
  end
  
  Foo.bar = 1

• Use OptionParser for parsing complex command line options and ruby -s for trivial command line options.

• Code in a functional way, avoiding mutation when that makes sense.

• Do not mutate parameters unless that is the purpose of the method.

• Avoid more than three levels of block nesting.

• Be consistent. In an ideal world, be consistent with these guidelines.

• Use common sense.

Tools

Here are some tools to help you automatically check Ruby code against this guide.

RuboCop

RuboCop is a Ruby code style checker based on this style guide. RuboCop already covers a significant portion of the Guide, supports both MRI 1.9 and MRI 2.0 and has good Emacs integration.

RubyMine

RubyMine's code inspections are partially based on this guide.

Contributing

The guide is still a work in progress—some rules are lacking examples, some rules don't have examples that illustrate them clearly enough. Improving such rules is a great (and simple way) to help the Ruby community!

In due time these issues will (hopefully) be addressed—just keep them in mind for now.

Nothing written in this guide is set in stone. It's my desire to work together with everyone interested in Ruby coding style, so that we could ultimately create a resource that will be beneficial to the entire Ruby community.

Feel free to open tickets or send pull requests with improvements. Thanks in advance for your help!

You can also support the project (and RuboCop) with financial contributions via Gratipay.

How to Contribute?

It's easy, just follow the contribution guidelines.

License

This work is licensed under a Creative Commons Attribution 3.0 Unported License

Spread the Word

A community-driven style guide is of little use to a community that doesn't know about its existence. Tweet about the guide, share it with your friends and colleagues. Every comment, suggestion or opinion we get makes the guide just a little bit better. And we want to have the best possible guide, don't we?

Cheers,
Bozhidar