The Ruby Style Guide

Prelude

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

One thing has always bothered me as a Ruby developer - Python developers have agreat 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 ofthe 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 complementaryRuby 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, and 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 1.9" 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 derivedfrom this guide). In the event of any conflicts, suchproject-specific guides take precedence for that project.

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

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

Translations of the guide are available in the following languages:

• Chinese Simplified
• Chinese Traditional
• French
• German
• Japanese
• Korean
• Portuguese
• Russian
• Spanish
• Vietnamese

Table of Contents

• Source Code Layout
• Syntax
• Naming
• Comments
  • Comment Annotations
• Classes
• Exceptions
• Collections
• Strings
• Regular Expressions
• Percent Literals
• Metaprogramming
• Misc
• Tools

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.^[link]

• Usetwospacesper indentation level (aka soft tabs). No hard tabs.^[link]

  # bad - four spacesdef some_method    do_somethingend# gooddef some_method  do_somethingend

• Use Unix-style line endings. (*BSD/Solaris/Linux/OS X users are covered by default, Windows users have to be extra careful.)^[link]

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

    $ git config --global core.autocrlf true
    

• Don't use; to separate statements and expressions. As a corollary - useone expression per line.^[link]

  # badputs 'foobar'; # superfluous semicolonputs 'foo'; puts 'bar' # two expressions on the same line# goodputs '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.^[link]

  # badclass FooError < StandardErrorend# okishclass FooError < StandardError; end# goodFooError = 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 theirvuse undesirable. At any rate - there should be no more than one expression in a single-line method.^[link]

  # baddef too_much; something; something_else; end# okish - notice that the first ; is requireddef no_braces_method; body end# okish - notice that the second ; is optionaldef no_braces_method; body; end# okish - valid syntax, but no ; makes it kind of hard to readdef some_method() body end# gooddef some_method  bodyend
  

  One exception to the rule are empty-body methods.

  # gooddef no_op; end
  

• Use spaces around operators, after commas, colons and semicolons, around{and before}. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code.^[link]

  sum = 1 + 2a, b = 1, 2[1, 2, 3].each { |e| puts e }class FooError < StandardError; end

  The only exception, regarding operators, is the exponent operator:

  # bade = M * c ** 2# goode = M * c**2

  { and } deserve a bit of clarification, since they are used for block and hash literals, as well as embedded expressions in strings. For hash literals two styles are considered acceptable.

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

  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.

  As far as embedded expressions go, there are also two acceptableoptions:

  # good - no spaces"string#{expr}"# ok - arguably more readable"string#{ expr }"
  

  The first style is extremely more popular and you're generally advised to stick with it. The second, on the other hand, is(arguably) a bit more readable. As with hashes - pick one styleand apply it consistently.

• No spaces after(,[ or before],).^[link]

  some(arg).other[1, 2, 3].size

• No space after!.^[link]

  # bad! something# good!something

• No space inside range literals.^[link]

  # bad1 .. 3'a' ... 'z'# good1..3'a'...'z'
  

• Indent when as deep as case. I know that many would disagree with this one, but it's the style established in both "The Ruby Programming Language" and "Programming Ruby".^[link]

  # badcase  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.playend# goodcasewhen 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.playend
  

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

  # bad - pretty convolutedkind = case yearwhen 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'endresult = if some_cond  calc_somethingelse  calc_something_elseend# good - it's apparent what's going onkind = 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'       endresult = 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'  endresult =  if some_cond    calc_something  else    calc_something_else  end
  

• Use empty linesbetween method definitions and also to break up a method into logical paragraphs internally.^[link]

  def some_method  data = initialize(options)  data.manipulate!  data.resultenddef some_method  resultend
  

• Avoid comma after the last parameter in a method call, especially when the parameters are not on separate lines.^[link]

  # bad - easier to move/add/remove parameters, but still not preferredsome_method(             size,             count,             color,           )# badsome_method(size, count, color, )# goodsome_method(size, count, color)

• Use spaces around the= operator when assigning default values to method parameters:^[link]

  # baddef some_method(arg1=:default, arg2=nil, arg3=[])  # do something...end# gooddef 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.^[link]

  # badresult = 1 - \         2# good (but still ugly as hell)result = 1 \         - 2long_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).^[link]

  • (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 lineone.two.three.  four# good - it's immediately clear what's going on the second lineone.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 continuesone.two.three  .four# good - it's immediately clear that the expression continues beyond the first lineone.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-lengthconstraints, single indent for the lines after the first is also acceptable.^[link]

  # starting point (line is too long)def send_mail(source)  Mailer.deliver(to: '[e-mail]', from: '[e-mail]', subject: 'Important message', body: source.text)end# bad (double indent)def send_mail(source)  Mailer.deliver(      to: '[e-mail]',      from: '[e-mail]',      subject: 'Important message',      body: source.text)end# gooddef send_mail(source)  Mailer.deliver(to: '[e-mail]',                 from: '[e-mail]',                 subject: 'Important message',                 body: source.text)end# good (normal indent)def send_mail(source)  Mailer.deliver(    to: '[e-mail]',    from: '[e-mail]',    subject: 'Important message',    body: source.text  )end
  

• Align the elements of array literals spanning multiple lines.^[link]

  # bad - single indentmenu_item = ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',  'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']# goodmenu_item = [  'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',  'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']# goodmenu_item =  ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',   'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']

• Addunderscores to large numeric literals to improve their readability.^[link]

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

• UseRDoc and its conventions for API documentation. Don't put an empty line between the comment block and the def.^[link]

• Limit lines to 80 characters.^[link]

• Avoid trailing whitespace.^[link]

• End each file with a newline.^[link]

• Don't use block comments. They cannot be preceded by whitespace and are not as easy to spot as regular comments.^[link]

  # bad=begincomment lineanother 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.^[link]

  # badSomeClass::some_methodsome_object::some_method# goodSomeClass.some_methodsome_object.some_methodSomeModule::SomeClass::SOME_CONSTSomeModule::SomeClass()

• Use def with parentheses when there are parameters. Omit the parentheses when the method doesn't accept any parameters.^[link]

  # baddef some_method() # body omittedend# gooddef some_method # body omittedend# baddef some_method_with_parameters param1, param2 # body omittedend# gooddef some_method_with_parameters(param1, param2) # body omittedend

• 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 -fordoesn't introduce a new scope (unlike each) and variables definedin its block will be visible outside it.^[link]

  arr = [1, 2, 3]# badfor elem in arr do  puts elemend# note that elem is accessible outside of the for loopelem # => 3# goodarr.each { |elem| puts elem }# elem is not accessible outside each's blockelem # => NameError: undefined local variable or method `elem'
  

• Do not use then for multi-line if/unless.^[link]

  # badif some_condition then  # body omittedend# goodif some_condition  # body omittedend
  

• Always put the condition on the same line as the if/unless in a multi-line conditional.^[link]

  # badif  some_condition  do_something  do_something_elseend# goodif some_condition  do_something  do_something_elseend
  

• Favor the ternary operator(?:) overif/then/else/end constructs.It's more common and obviously more concise.^[link]

  # badresult = if some_condition then something else something_else end# goodresult = 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.^[link]

  # badsome_condition ? (nested_condition ? nested_something : nested_something_else) : something_else# goodif some_condition  nested_condition ? nested_something : nested_something_elseelse  something_elseend
  

• Do not use if x; .... Use the ternary operator instead.^[link]

  # badresult = if some_condition; something else something_else end# goodresult = some_condition ? something : something_else

• Leverage the fact that if andcase are expressions which return a result.^[link]

  # badif condition  result = xelse  result = yend# goodresult =  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.^[link]

• Do not use when x; .... See the previous rule.^[link]

• Use! instead ofnot.^[link]

  # bad - braces are required because of op precedencex = (not something)# goodx = !something

• Avoid the use of!!.^[link]

  # badx = 'test'# obscure nil checkif !!x  # body omittedendx = false# double negation is useless on booleans!!x # => false# goodx = 'test'unless x.nil?  # body omittedend
  

• The and and or keywords are banned. It's just not worth it. Always use&& and|| instead.^[link]

  # bad# boolean expressionif some_condition and some_other_condition  do_somethingend# control flowdocument.saved? or document.save!# good# boolean expressionif some_condition && some_other_condition  do_somethingend# control flowdocument.saved? || document.save!

• Avoid multi-line ?: (the ternary operator); useif/unless instead.^[link]
  

• Favor modifier if/unless usage when you have a single-line body. Another good alternative is the usage of control flow&&/||.^[link]

  # badif some_condition  do_somethingend# gooddo_something if some_condition# another good optionsome_condition && do_something

• Avoid modifierif/unless usage at the end of a non-trivial multi-lineblock.^[link]

  # bad10.times do  # multi-line body omittedend if some_condition# goodif some_condition  10.times do    # multi-line body omitted  endend
  

• Favorunless overif fornegative conditions (or control flow||).^[link]

  # baddo_something if !some_condition# baddo_something if not some_condition# gooddo_something unless some_condition# another good optionsome_condition || do_something

• Do not use unless with else. Rewrite these with the positive case first.^[link]

  # badunless success?  puts 'failure'else  puts 'success'end# goodif success?  puts 'success'else  puts 'failure'end
  

• Don't use parentheses around the condition of an if/unless/while/until.^[link]

  # badif (x > 10)  # body omittedend# goodif x > 10  # body omittedend
  

Note that there is an exception to this rule, namely safe assignment incondition.

• Do not use while/until condition do for multi-line while/until.^[link]

  # badwhile x > 5 do  # body omittedenduntil x > 5 do  # body omittedend# goodwhile x > 5  # body omittedenduntil x > 5  # body omittedend
  

• Favor modifier while/until usage when you have asingle-line body.^[link]

  # badwhile some_condition  do_somethingend# gooddo_something while some_condition
  
  

• Favoruntil over while for negative conditions.^[link]

  # baddo_something while !some_condition# gooddo_something until some_condition
  
  

• Use Kernel#loop instead of while/until when you need an infinite loop.^[link]

  # badwhile true  do_somethingenduntil false  do_somethingend# goodloop do  do_somethingend
  

• UseKernel#loop with break rather than begin/end/until or begin/end/while for post-loop tests.^[link]

  # badbegin  puts val  val += 1end while val < 0# goodloop do  puts val  val += 1  break unless val < 0end
  

• Omit parentheses around parameters formethods that are part of an internal DSL (e.g. Rake, Rails, RSpec), methods that have "keyword" status in Ruby(e.g.attr_reader,puts) andattribute access methods. Use parentheses around the arguments of all other method invocations.^[link]

  class Person  attr_reader :name, :age  # omittedendtemperance = Person.new('Temperance', 30)temperance.nameputs temperance.agex = Math.sin(y)array.delete(e)bowling.score.should == 0
  

• Omit the outer braces around an implicit options hash.^[link]

  # baduser.set({ name: 'John', age: 45, permissions: { read: true } })# gooduser.set(name: 'John', age: 45, permissions: { read: true })
  
  

• Omit both the outer braces and parentheses for methods that are part of an internal DSL.^[link]

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

• Omit parentheses for method calls with no arguments.^[link]

  # badKernel.exit!()2.even?()fork()'test'.upcase()# goodKernel.exit!2.even?fork'test'.upcase
  
  

• Prefer{...} overdo...end for single-line blocks. Avoid using{...}for multi-line blocks (multiline 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.^[link]

  names = ['Bozhidar', 'Steve', 'Sarah']# badnames.each do |name|  puts nameend# goodnames.each { |name| puts name }# badnames.select do |name|  name.start_with?('S')end.map { |name| name.upcase }# goodnames.select { |name| name.start_with?('S') }.map { |name| name.upcase }

  Some will argue that multiline 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?

• Consider using explicit block argument to avoid writing block literal that just passes its arguments to another block. Be ware of the performance impact,though, as the block gets converted to a Proc.^[link]

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

• Avoidreturn where not required for flow of control.^[link]

  # baddef some_method(some_arr)  return some_arr.sizeend# gooddef some_method(some_arr)  some_arr.sizeend
  

• Avoidself where not required. (It is only required when calling a self write accessor.)^[link]

  # baddef ready?  if self.last_reviewed_at > self.last_updated_at    self.worker.update(self.content, self.options)    self.status = :in_progress  end  self.status == :verifiedend# gooddef ready?  if last_reviewed_at > last_updated_at    worker.update(content, options)    self.status = :in_progress  end  status == :verifiedend
  

• As a corollary, avoid shadowing methods with local variables unless they are both equivalent.^[link]

  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  endend
  

• 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 incondition.^[link]

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

• Useshort hand self assignment operators whenever applicable.^[link]

  # badx = x + yx = x * yx = x**yx = x / yx = x || yx = x && y# goodx += yx *= yx **= yx /= yx ||= yx &&= y
  
  

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

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

• Don't use||= to initialize boolean variables. (Consider what would happenif the current value happened to befalse.)^[link]

  # bad - would set enabled to true even if it was falseenabled ||= true# goodenabled = 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.^[link]

  # badif something  something = something.downcaseend# badsomething = something ? something.downcase : nil# oksomething = something.downcase if something# goodsomething = something && something.downcase# bettersomething &&= something.downcase
  
  

• Avoid explicit use of the case equality operator ===. As its name impliesit is meant to be used implicitly by case expressions and outside of them ityields some pretty confusing code.^[link]

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

• Do not use eql? when using== will do. The stricter comparison semanticsprovided byeql? are rarely needed in practice.^[link]

  # bad - eql? is the same as == for strings"ruby".eql? some_str# good"ruby" == some_str1.0.eql? x # eql? makes sense here if want to differentiate between Fixnum and Float 1
  

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

  # bad$:.unshift File.dirname(__FILE__)# goodrequire 'English'$LOAD_PATH.unshift File.dirname(__FILE__)
  
  

• Do not put aspace between a method name and the opening parenthesis.^[link]

  # badf (3 + 2) + 1# goodf(3 + 2) + 1
  

• If the first argument to a method begins with an open parenthesis, always use parentheses in the method invocation. For example, write f((3 + 2) + 1).^[link]

• Always run the Ruby interpreter with the-w option so it will warn you if you forget either of the rules above!^[link]

• Use the new lambda literal syntax for single line body blocks. Use the lambda method for multi-line blocks.^[link]

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

• Prefer proc over Proc.new.^[link]

  # badp = Proc.new { |n| puts n }# goodp = proc { |n| puts n }
  
  

• Prefer proc.call() over proc[] or proc.() for both lambdas and procs.^[link]

  # bad - looks similar to Enumeration accessl = ->(v) { puts v }l[1]# also bad - uncommon syntaxl = ->(v) { puts v }l.(1)# goodl = ->(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.^[link]

  # badresult = hash.map { |k, v| v + 1 }def something(x)  unused_var, used_var = something_else(x)  # ...end# goodresult = hash.map { |_k, v| v + 1 }def something(x)  _unused_var, used_var = something_else(x)  # ...end# goodresult = hash.map { |_, v| v + 1 }def something(x)  _, used_var = something_else(x)  # ...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.^[link]

• 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 thewarn level to 0 via-W0).^[link]

• Favor the use of sprintf and its alias format over the fairly crypticString#% method.^[link]

  # bad'%d %d' % [20, 10]# => '20 10'# goodsprintf('%d %d', 20, 10)# => '20 10'# goodsprintf('%{first} %{second}', first: 20, second: 10)# => '20 10'format('%d %d', 20, 10)# => '20 10'# goodformat('%{first} %{second}', first: 20, second: 10)# => '20 10'
  

• Favor the use of Array#join over the fairly cryptic Array#* with^[link]a string argument.

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

• Use [*var] or Array() instead of explicit Array check, when dealing with a variable you want to treat as an Array, but you're not certain it's an array.^[link]

  # badpaths = [paths] unless paths.is_a? Arraypaths.each { |path| do_something(path) }# good[*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.^[link]

  # baddo_something if x >= 1000 && x <= 2000# gooddo_something if (1000..2000).include?(x)# gooddo_something if x.between?(1000, 2000)
  
  

• Favor the use of predicate methods to explicit comparisons with==.Numeric comparisons are OK.^[link]

  # badif x % 2 == 0endif x % 2 == 1endif x == nilend# goodif x.even?endif x.odd?endif x.nil?endif x.zero?endif x == 0end
  

• Don't do explicit non-nil checks unless you're dealing with boolean values.^[link]

  # baddo_something if !something.nil?do_something if something != nil# gooddo_something if something# good - dealing with a booleandef value_set?  !@some_boolean.nil?end
  

• Avoid the use ofBEGIN blocks.^[link]

• Do not use END blocks. Use Kernel#at_exit instead.^[link]

  # badEND { puts 'Goodbye!' }# goodat_exit { puts 'Goodbye!' }
  
  

• Avoid the use of flip-flops.^[link]

• Avoid use of nested conditionals for flow of control.^[link]

  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.

  # baddef compute_thing(thing)  if thing[:foo]    update_with_bar(thing)    if thing[:foo][:bar]      partial_compute(thing)    else      re_compute(thing)    end  endend# gooddef 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  endend# good[0, 1, 2, 3].each do |item|  next unless item > 1  puts itemend
  

• Prefermap over collect,find over detect,select over find_all,reduce over inject and size over length. This is not a hardr equirement; 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.^[link]

• 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 it‘s size.^[link]

  # badsome_hash.count# goodsome_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.^[link]

  # badall_songs = users.map(&:songs).flatten.uniq# goodall_songs = users.flat_map(&:songs).uniq
  
  

• Use reverse_each instead of reverse.each. reverse_each doesn't do anew array allocation and that's a good thing.^[link]

  # badarray.reverse.each { ... }# goodarray.reverse_each { ... }
  
  

Naming

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

• Name identifiers in English.^[link]

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

• Use snake_case for symbols, methods and variables.^[link]

  # bad:'some symbol':SomeSymbol:someSymbolsomeVar = 5def someMethod  ...enddef SomeMethod...end# good:some_symboldef some_method  ...end
  

• UseCamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XMLuppercase.)^[link]

  # badclass Someclass  ...endclass Some_Class  ...endclass SomeXml  ...end# goodclass SomeClass  ...endclass SomeXML  ...end
  

• Use snake_case for naming files, e.g.hello_world.rb.^[link]

• Use snake_case for naming directories, e.g.lib/hello_world/hello_world.rb.^[link]

• 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.^[link]

• Use SCREAMING_SNAKE_CASE for other constants.^[link]

  # badSomeConst = 5# goodSOME_CONST = 5
  

• 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.^[link]

• The names of potentially dangerous methods (i.e. methods that modify self or the arguments,exit! (doesn't run the finalizers like exitdoes), etc.) should end with an exclamation mark if there exists a safe version of that dangerous method.^[link]

  # bad - there is no matching 'safe' methodclass Person  def update!  endend# goodclass Person  def update  endend# goodclass Person  def update!  end  def update  endend
  

• Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.^[link]

  class Array  def flatten_once!    res = []    each do |e|      [*e].each { |f| res << f }    end    replace(res)  end  def flatten_once    dup.flatten_once!  endend
  

• When using reduce with short blocks, name the arguments|a, e|(accumulator, element).^[link]

• When defining binary operators, name the parameterother(<< and[] are exceptions to the rule, since their semantics are different).^[link]

  def +(other)  # body omittedend
  

Comments

Good code is its own best documentation. As you're about to add acomment, ask yourself, "How can I improve the code so that thiscomment isn't needed?" Improve the code and then document it to makeit even clearer.
-- Steve McConnell

• Write self-documenting code and ignore the rest of this section. Seriously!^[link]

• Write comments in English.^[link]

• Use one space between the leading# character of the comment and the textof the comment.^[link]

• Comments longer than a word are capitalized and use punctuation. Useonespace after periods.^[link]

• Avoid superfluous comments.^[link]

  # badcounter += 1 # Increments counter by one.

• Keep existing comments up-to-date. An outdated comment is worse than nocomment at all.^[link]

Good code is like a good joke - it needs no explanation.
-- Russ Olsen

• Avoid writing comments to explain bad code. Refactor the code to make itself-explanatory. (Do or do not - there is no try. --Yoda)^[link]

Comment Annotations

• Annotations should usually be written on the line immediately above therelevant code.^[link]

• The annotation keyword is followed by a colon and a space, then a notedescribing the problem.^[link]

• If multiple lines are required to describe the problem, subsequent linesshould be indented two spaces after the#.^[link]

  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 beredundant, annotations may be left at the end of the offending line with nonote. This usage should be the exception and not the rule.^[link]

  def bar  sleep 100 # OPTIMIZEend

• Use TODO to note missing features or functionality that should be added ata later date.^[link]

• Use FIXME to note broken code that needs to be fixed.^[link]

• Use OPTIMIZE to note slow or inefficient code that may cause performanceproblems.^[link]

• Use HACK to note code smells where questionable coding practices were usedand should be refactored away.^[link]

• Use REVIEW to note anything that should be looked at to confirm it isworking as intended. For example:REVIEW: Are we sure this is how the clientdoes X currently?^[link]

• Use other custom annotation keywords if it feels appropriate, but be sure todocument them in your project'sREADME or similar.^[link]

Classes & Modules

• Use a consistent structure in your class definitions.^[link]

  class Person  # extend and include go first  extend SomeModule  include AnotherModule  # inner classes  CustomErrorKlass = 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  # followed by 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  endend

• Don't nest multi line classes within classes. Try to have such nestedclasses each in their own file in a folder named like the containing class.^[link]

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

• Prefer modules to classes with only class methods. Classes should be usedonly when it makes sense to create instances out of them.^[link]

  # badclass SomeClass  def self.some_method    # body omitted  end  def self.some_other_method  endend# goodmodule SomeModule  module_function  def some_method    # body omitted  end  def some_other_method  endend

• Favor the use ofmodule_function overextend self when you want to turna module's instance methods into class methods.^[link]

  # badmodule Utilities  extend self  def parse_something(string)    # do stuff here  end  def other_utility_method(number, string)    # do some more stuff  endend# goodmodule Utilities  module_function  def parse_something(string)    # do stuff here  end  def other_utility_method(number, string)    # do some more stuff  endend

• When designing class hierarchies make sure that they conform to theLiskovSubstitutionPrinciple.^[link]

• Try to make your classes asSOLID aspossible.^[link]

• Always supply a properto_s method for classes that represent domainobjects.^[link]

  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}"  endend

• Use theattr family of functions to define trivial accessors or mutators.^[link]

  # badclass 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  endend# goodclass Person  attr_reader :first_name, :last_name  def initialize(first_name, last_name)    @first_name = first_name    @last_name = last_name  endend

• Avoid the use ofattr. Useattr_reader andattr_accessor instead.^[link]

  # bad - creates a single attribute accessor (deprecated in 1.9)attr :something, trueattr :one, :two, :three # behaves as attr_reader# goodattr_accessor :somethingattr_reader :one, :two, :three

• Consider usingStruct.new, which defines the trivial accessors,constructor and comparison operators for you.^[link]

  # goodclass Person  attr_accessor :first_name, :last_name  def initialize(first_name, last_name)    @first_name = first_name    @last_name = last_name  endend# betterPerson = Struct.new(:first_name, :last_name) doend

• Don't extend aStruct.new - it already is a new class. Extending itintroduces a superfluous class level and may also introduce weird errors ifthe file is required multiple times.^[link]

• Consider adding factory methods to provide additional sensible ways tocreate instances of a particular class.^[link]

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

• Prefer duck-typing overinheritance.^[link]

  # badclass Animal  # abstract method  def speak  endend# extend superclassclass Duck < Animal  def speak    puts 'Quack! Quack'  endend# extend superclassclass Dog < Animal  def speak    puts 'Bau! Bau!'  endend# goodclass Duck  def speak    puts 'Quack! Quack'  endendclass Dog  def speak    puts 'Bau! Bau!'  endend

• Avoid the usage of class (@@) variables due to their "nasty" behavior ininheritance.^[link]

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

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

• Assign proper visibility levels to methods (private,protected) inaccordance with their intended usage. Don't go off leaving everythingpublic(which is the default). After all we're coding in Ruby now, not inPython.^[link]

• Indent thepublic,protected, andprivate methods as much the methoddefinitions they apply to. Leave one blank line above the visibility modifierand one blank line below in order to emphasize that it applies to all methodsbelow it.^[link]

  class SomeClass  def public_method    # ...  end  private  def private_method    # ...  end  def another_private_method    # ...  endend

• Usedef self.method to define singleton methods. This makes the codeeasier to refactor since the class name is not repeated.^[link]

  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 singleton methods.  class << self    def first_method      # body omitted    end    def second_method_etc      # body omitted    end  endend

• Preferalias when aliasing methods in lexical class scope as theresolution ofself in this context is also lexical, and it communicatesclearly to the user that the indirection of your alias will not be alteredat runtime or by any subclass unless made explicit.^[link]

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

  Since alias, like def, is a keyword, prefer bareword arguments oversymbols or strings. In other words, doalias foo bar, notalias :foo :bar.

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

  class Fugitive < Westerner  def first_name    'Nobody'  endend

  In this example, Fugitive#given_name would still call the originalWesterner#first_name method, notFugitive#first_name. To override thebehavior ofFugitive#given_name as well, you'd have to redefine it in thederived class.

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

• Always usealias_method when aliasing methods of modules, classes, orsingleton classes at runtime, as the lexical scope ofalias leads tounpredictability in these cases.^[link]

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

Exceptions

• Signal exceptions using thefail method. Useraise only when catching anexception and re-raising it (because here you're not failing, but explicitlyand purposefully raising an exception).^[link]

  begin  fail 'Oops'rescue => error  raise if error.message != 'Oops'end

• Don't specifyRuntimeError explicitly in the two argument version offail/raise.^[link]

  # badfail RuntimeError, 'message'# good - signals a RuntimeError by defaultfail 'message'

• Prefer supplying an exception class and a message as two separate argumentstofail/raise, instead of an exception instance.^[link]

  # badfail SomeException.new('message')# Note that there is no way to do `fail SomeException.new('message'), backtrace`.# goodfail SomeException, 'message'# Consistent with `fail SomeException, 'message', backtrace`.

• Do not return from anensure block. If you explicitly return from a methodinside anensure block, the return will take precedence over any exceptionbeing raised, and the method will return as if no exception had been raised atall. In effect, the exception will be silently thrown away.^[link]

  def foo  failensure  return 'very bad idea'end

• Use implicit begin blocks where possible.^[link]

  # baddef foo  begin    # main logic goes here  rescue    # failure handling goes here  endend# gooddef foo  # main logic goes hererescue  # failure handling goes hereend

• Mitigate the proliferation ofbegin blocks by usingcontingency methods(a term coined by Avdi Grimm).^[link]

  # badbegin  something_that_might_failrescue IOError  # handle IOErrorendbegin  something_else_that_might_failrescue IOError  # handle IOErrorend# gooddef with_io_error_handling   yieldrescue IOError  # handle IOErrorendwith_io_error_handling { something_that_might_fail }with_io_error_handling { something_else_that_might_fail }

• Don't suppress exceptions.^[link]

  # badbegin  # an exception occurs hererescue SomeError  # the rescue clause does absolutely nothingend# baddo_something rescue nil

• Avoid usingrescue in its modifier form.^[link]

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

• Don't use exceptions for flow of control.^[link]

  # badbegin  n / drescue ZeroDivisionError  puts 'Cannot divide by 0!'end# goodif d.zero?  puts 'Cannot divide by 0!'else  n / dend

• Avoid rescuing theException class. This will trap signals and calls toexit, requiring you tokill -9 the process.^[link]

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

• Put more specific exceptions higher up the rescue chain, otherwise they'llnever be rescued from.^[link]

  # badbegin  # some coderescue Exception => e  # some handlingrescue StandardError => e  # some handling that will never be executedend# goodbegin  # some coderescue StandardError => e  # some handlingrescue Exception => e  # some handlingend

• Release external resources obtained by your program in an ensure block.^[link]

  f = File.open('testfile')begin  # .. processrescue  # .. handle errorensure  f.close if fend

• Favor the use of exceptions for the standard library over introducing newexception classes.^[link]

Collections

• Prefer literal array and hash creation notation (unless you need to passparameters to their constructors, that is).^[link]

  # badarr = Array.newhash = Hash.new# goodarr = []hash = {}

• 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 thisrule only to arrays with two or more elements.^[link]

  # badSTATES = ['draft', 'open', 'closed']# goodSTATES = %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 onlyto arrays with two or more elements.^[link]

  # badSTATES = [:draft, :open, :closed]# goodSTATES = %i(draft open closed)

• Avoid comma after the last item of anArray orHash literal, especiallywhen the items are not on separate lines.^[link]

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

• Avoid the creation of huge gaps in arrays.^[link]

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

• When accessing the first or last element from an array, preferfirst orlast over[0] or[-1].^[link]

• Use Set instead ofArray when dealing with unique elements. Setimplements a collection of unordered values with no duplicates. This is ahybrid ofArray's intuitive inter-operation facilities andHash's fastlookup.^[link]

• Prefer symbols instead of strings as hash keys.^[link]

  # badhash = { 'one' => 1, 'two' => 2, 'three' => 3 }# goodhash = { one: 1, two: 2, three: 3 }

• Avoid the use of mutable objects as hash keys.^[link]

• Use the Ruby 1.9 hash literal syntax when your hash keys are symbols.^[link]

  # badhash = { :one => 1, :two => 2, :three => 3 }# goodhash = { one: 1, two: 2, three: 3 }

• Don't mix the Ruby 1.9 hash syntax with hash rockets in the same hashliteral. When you've got keys that are not symbols stick to the hash rocketssyntax.^[link]

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

• Use Hash#key? instead ofHash#has_key? and Hash#value? instead ofHash#has_value?. As notedhere byMatz, the longer forms are considered deprecated.^[link]

  # badhash.has_key?(:test)hash.has_value?(value)# goodhash.key?(:test)hash.value?(value)

• Use Hash#fetch when dealing with hash keys that should be present.^[link]

  heroes = { batman: 'Bruce Wayne', superman: 'Clark Kent' }# bad - if we make a mistake we might not spot it right awayheroes[:batman] # => "Bruce Wayne"heroes[:supermann] # => nil# good - fetch raises a KeyError making the problem obviousheroes.fetch(:supermann)

• Introduce default values for hash keys viaHash#fetch as opposed to usingcustom logic.^[link]

  batman = { name: 'Bruce Wayne', is_evil: false }# bad - if we just use || operator with falsy value we won't get the expected resultbatman[:is_evil] || true # => true# good - fetch work correctly with falsy valuesbatman.fetch(:is_evil, true) # => false

• Prefer the use of the block instead of the default value inHash#fetch.^[link]

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

• Use Hash#values_at when you need to retrieve several values consecutivelyfrom a hash.^[link]

  # bademail = data['email']username = data['nickname']# goodemail, username = data.values_at('email', 'nickname')

• Rely on the fact that as of Ruby 1.9 hashes are ordered.^[link]

• Do not modify a collection while traversing it.^[link]

Strings

• Prefer string interpolation and string formatting instead of stringconcatenation:^[link]

  # bademail_with_name = user.name + ' <' + user.email + '>'# goodemail_with_name = "#{user.name} <#{user.email}>"# goodemail_with_name = format('%s <%s>', user.name, user.email)

• Consider padding string interpolation code with space. It more clearly setsthe code apart from the string.^[link]

  "#{ user.last_name }, #{ user.first_name }"

• Adopt a consistent string literal quoting style. There are two popularstyles in the Ruby community, both of which are considered good - singlequotes by default (Option A) and double quotes by default (Option B).^[link]

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

    # badname = "Bozhidar"# goodname = 'Bozhidar'

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

    # badname = 'Bozhidar'# goodname = "Bozhidar"

  The second style is arguably a bit more popular in the Rubycommunity. The string literals in this guide, however, arealigned with the first style.

• Don't use the character literal syntax?x. Since Ruby 1.9 it's basicallyredundant -?x would interpreted as'x' (a string with a single characterin it).^[link]

  # badchar = ?c# goodchar = 'c'

• Don't leave out{} around instance and global variables being interpolatedinto a string.^[link]

  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}"  endend$global = 0# badputs "$global = #$global"# goodputs "$global = #{$global}"

• Don't use Object#to_s on interpolated objects. It's invoked on themautomatically.^[link]

  # badmessage = "This is the #{result.to_s}."# goodmessage = "This is the #{result}."

• Avoid usingString#+ when you need to construct large data chunks.Instead, useString#<<. Concatenation mutates the string instance in-placeand is always faster thanString#+, which creates a bunch of new stringobjects.^[link]

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

• Don't useString#gsub in scenarios in which you can use a faster more specialized alternative.^[link]

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

• When using heredocs for multi-line strings keep in mind the fact that theypreserve leading whitespace. It's a good practice to employ some margin basedon which to trim the excessive whitespace.^[link]

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

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']^[link]

• For simple constructions you can use regexp directly through string index.^[link]

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

• Use non-capturing groups when you don't use captured result of parentheses.^[link]

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

• Don't use the cryptic Perl-legacy variables denoting last regexp groupmatches ($1,$2, etc). UseRegexp.last_match[n] instead.^[link]

  /(regexp)/ =~ string...# badprocess $1# goodprocess Regexp.last_match[1]

• Avoid using numbered groups as it can be hard to track what they contain.Named groups can be used instead.^[link]

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

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

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

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

• Usex modifier for complex regexps. This makes them more readable and youcan add some useful comments. Just be careful as spaces are ignored.^[link]

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

• For complex replacementssub/gsub can be used with block or hash.^[link]

Percent Literals

• Use%()(it's a shorthand for%Q) for single-line strings which requireboth interpolation and embedded double-quotes. For multi-line strings, preferheredocs.^[link]

  # 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 %q unless you have a string with both' and " in it. Regularstring literals are more readable and should be preferred unless a lot ofcharacters would have to be escaped in them.^[link]

  # badname = %q(Bruce Wayne)time = %q(8 o'clock)question = %q("What did you say?")# goodname = 'Bruce Wayne'time = "8 o'clock"question = '"What did you say?"'

• Use %r only for regular expressions matchingmore than one '/'character.^[link]

  # bad%r(\s+)# still bad%r(^/(.*)$)# should be /^\/(.*)$/# good%r(^/blog/2011/(.*)$)

• Avoid the use of%x unless you're going to invoke a command withbackquotes in it(which is rather unlikely).^[link]

  # baddate = %x(date)# gooddate = `date`echo = %x(echo `date`)

• Avoid the use of%s. It seems that the community has decided:"somestring" is the preferred way to create a symbol with spaces in it.^[link]

• Prefer() as delimiters for all% literals, except%r. Since parenthesesoften appear inside regular expressions in many scenarios a less commoncharacter like{ might be a better choice for a delimiter, depending on theregexp's content.^[link]

  # bad%w[one two three]%q{"Test's king!", John said.}# good%w(one two three)%q("Test's king!", John said.)

Metaprogramming

• Avoid needless metaprogramming.^[link]

• Do not mess around in core classes when writing libraries. (Do notmonkey-patch them.)^[link]

• The block form ofclass_eval is preferable to the string-interpolatedform. - when you use the string-interpolated form, always supply__FILE__and__LINE__, so that your backtraces make sense:^[link]

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

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

• When usingclass_eval (or othereval) with string interpolation, add acomment block showing its appearance if interpolated (a practice used in Railscode):^[link]

  # from activesupport/lib/active_support/core_ext/string/output_safety.rbUNSAFE_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  endend

• Avoid usingmethod_missing for metaprogramming because backtraces becomemessy, the behavior is not listed in#methods, and misspelled method callsmight silently work, e.g.nukes.launch_state = false. Consider usingdelegation, proxy, ordefine_method instead. If you must usemethod_missing:^[link]

  • 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:

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

• Preferpublic_send oversend so as not to circumventprivate/protected visibility.^[link]

Misc

• Write ruby -w safe code.^[link]

• Avoid hashes as optional parameters. Does the method do too much? (Objectinitializers are exceptions for this rule).^[link]

• Avoid methods longer than 10 LOC (lines of code). Ideally, most methods willbe shorter than 5 LOC. Empty lines do not contribute to the relevant LOC.^[link]

• Avoid parameter lists longer than three or four parameters.^[link]

• If you really need "global" methods, add them to Kernel and make themprivate.^[link]

• Use module instance variables instead of global variables.^[link]

  # bad$foo_bar = 1# goodmodule Foo  class << self    attr_accessor :bar  endendFoo.bar = 1

• Use OptionParser for parsing complex command line options andruby -sfor trivial command line options.^[link]

• Prefer Time.now overTime.new when retrieving the current system time.^[link]

• Code in a functional way, avoiding mutation when that makes sense.^[link]

• Do not mutate parameters unless that is the purpose of the method.^[link]

• Avoid more than three levels of block nesting.^[link]

• Be consistent. In an ideal world, be consistent with these guidelines.^[link]

• Use common sense.^[link]

Tools

Here's some tools to help you automatically check Ruby code againstthis guide.

RuboCop

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

RubyMine

RubyMine's code inspections arepartially basedon this guide.

Contributing

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

In due time these issues will (hopefully) be addressed - just keep them in mindfor now.

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

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

You can also support the project (and RuboCop) with financialcontributions viagittip.

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 thatdoesn't know about its existence. Tweet about the guide, share it withyour friends and colleagues. Every comment, suggestion or opinion weget makes the guide just a little bit better. And we want to have thebest possible guide, don't we?

Cheers,
Bozhidar

转自 https://github.com/bbatsov/ruby-style-guide#syntax