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Much of this was taken from https://github.com/bbatsov/ruby-style-guide and https://github.com/styleguide/ruby.

Table of Contents

Source Code Layout

  • Use UTF-8 as the source file encoding.

  • Use two spaces per indentation level. No hard tabs.

    # bad - four spaces
    def some_method
        do_something
    end
    
    # good
    def some_method
      do_something
    end
    
  • Avoid single-line methods.

    # 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 ; make 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, around { and before }. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code.

    sum = 1 + 2
    a, b = 1, 2
    1 > 2 ? true : false; puts 'Hi'
    [1, 2, 3].each { |e| puts e }
    
  • The only exceptions, are the exponent operator and string interpolation:

  • The exponent operator should have no spaces around it.

    # bad
    e = M * c ** 2
    
    # good
    e = M * c**2
    
  • String interpolation should have no spaces after #{ or before }.

    # bad
    "string#{ expr }"
    
    # good - no spaces
    "string#{expr}"
    
  • No spaces after (, [ or before ], ).

    some(arg).other
    [1, 2, 3].length
    
  • Indent when as deep as case.

    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
    
    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
    
  • Use empty lines between defs and to break up a method into logical paragraphs.

    def some_method
      data = initialize(options)
    
      data.manipulate!
    
      data.result
    end
    
    def some_method
      result
    end
    
  • Don't 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
    
  • Avoid line continuation \ where not required. In practice, avoid using line continuations at all.

    # bad
    result = 1 - \
             2
    
    # good (but still ugly as hell)
    result = 1 \
             - 2
    
  • 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
    
  • Align multi-line parameters with one indent at the level of the method callee. Each parameter and the closing parenthesis should be on their own line

    # 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)
    def send_mail(source)
      Mailer.deliver(
          to: 'bob@example.com',
          from: 'us@example.com',
          subject: 'Important message',
          body: source.text
      )
    end
    
    # good (normal indent aligned to callee)
    def send_mail(source)
      Mailer.deliver(
        to: 'bob@example.com',
        from: 'us@example.com',
        subject: 'Important message',
        body: source.text
      )
    end
    
    # good (normal indent aligned to callee)
    def send_mail(source)
      mail = Mailer.deliver(
               to: 'bob@example.com',
               from: 'us@example.com',
               subject: 'Important message',
               body: source.text
             )
    end
    
  • Add underscores to large numeric literals to improve their readability.

    # bad - how many 0s are there?
    num = 1000000
    
    # good - much easier to parse for the human brain
    num = 1_000_000
    
  • Limit lines to 120 characters.

  • Remove all trailing whitespace.

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

    # bad
    == begin
    comment line
    another comment line
    == end
    
    # good
    # comment line
    # another comment line
    
  • Leave an empty line at the end of files.

Syntax

  • Use :: only to reference constants(this includes classes and modules). Never use :: for method invocation.

    # bad
    SomeClass::some_method
    some_object::some_method
    
    # good
    SomeClass.some_method
    some_object.some_method
    SomeModule::SomeClass::SOME_CONST
    
  • Use def with parentheses when there are arguments. Omit the parentheses when the method doesn't accept any arguments.

    # bad
    def some_method()
     # body omitted
    end
    
    # good
    def some_method
     # body omitted
    end
    
    # bad
    def some_method_with_arguments arg1, arg2
     # body omitted
    end
    
    # good
    def some_method_with_arguments(arg1, arg2)
     # body omitted
    end
    
  • Never use then for multi-line if/unless.

    # bad
    if some_condition then
      # body omitted
    end
    
    # good
    if some_condition
      # body omitted
    end
    
  • Favor the ternary operator(?:) over if/then/else/end constructs

    # 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.

    # 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
    
  • Use ! instead of not.

    # bad - braces are required because of op precedence
    x = (not something)
    
    # good
    x = !something
    
  • The and and or keywords are banned. It's just not worth it. Always use && and || instead.

    # bad
    # boolean expression
    if some_condition and some_other_condition
      do_something
    end
    
    # control flow
    document.saved? or document.save!
    
    # good
    # boolean expression
    if some_condition && some_other_condition
      do_something
    end
    
    # control flow
    document.saved? || document.save!
    
  • Do not use multi-line ?: (the ternary operator); use if/unless instead.

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

    # bad
    if some_condition
      do_something
    end
    
    # good
    do_something if some_condition
    
    # another good option
    some_condition && do_something
    
    # bad
    while some_condition
      do_something
    end
    
    # good
    do_something while some_condition
    
  • Favor unless over if for negative conditions (or control flow ||). Also Favor until over while for negative conditions.

    # 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
    
    # bad
    do_something while !some_condition
    
    # good
    do_something until some_condition
    
  • Never use unless with else. Rewrite these with the positive case first.

    # 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 an if/unless/while, unless the condition contains an assignment.

    # bad
    if (x > 10)
      # body omitted
    end
    
    # good
    if x > 10
      # body omitted
    end
    
    # ok
    if (x = self.next_value)
      # body omitted
    end
    
  • Don't use the return value of = (an assignment) in conditional expressions.

    # bad (+ a warning)
    if (v = array.grep(/foo/))
      do_something(v)
      ...
    end
    
    # bad (+ a warning)
    if v = array.grep(/foo/)
      do_something(v)
      ...
    end
    
    # good
    v = array.grep(/foo/)
    if v
      do_something(v)
      ...
    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 parentheses around parameters for methods that are part of an internal DSL (e.g. Rake, Rails, RSpec), methods that have "keyword" status in Ruby (e.g. attr_reader, puts) and attribute access methods. Use parentheses around the arguments of all other method invocations.

    class Person
      attr_reader :name, :age
    
      # omitted
    end
    
    temperance = Person.new('Temperance', 30)
    temperance.name
    
    puts temperance.age
    
    x = Math.sin(y)
    array.delete(e)
    
    bowling.score.should == 0
    
  • Omit parentheses for method calls with no arguments.

    # bad
    Kernel.exit!()
    2.even?()
    fork()
    'test'.upcase()
    
    # good
    Kernel.exit!
    2.even?
    fork
    'test'.upcase
    
  • Prefer {...} over do...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.

    names = ['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 { |name| name.upcase }
    
  • Avoid return where not required for flow of control.

    # 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)

    # 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
    
  • Avoid shadowing methods with local variables unless they are both equivalent.

    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
    
  • Use ||= freely to initialize variables.

    # 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.)

    # bad - would set enabled to true even if it was false
    enabled ||= true
    
    # good
    enabled = true if enabled.nil?
    
  • Prefer proc over Proc.new.

    # bad
    p = Proc.new { |n| puts n }
    
    # good
    p = proc { |n| puts n }
    
  • Use _ for unused block parameters.

    # bad
    result = hash.map { |k, v| v + 1 }
    
    # good
    result = hash.map { |_, v| v + 1 }
    
  • 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.

    # bad
    paths = [paths] unless paths.is_a? Array
    paths.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 instead of complex comparison logic when possible.

    # bad
    do_something if x >= 1000 && x < 2000
    
    # good
    do_something if (1000...2000).include?(x)
    
  • Prefer the -> operator over lambda for creating Procs

    # bad
    be_awesome = lambda {|word| puts "#{word} is awesome!" }
    
    # good
    be_awesome = ->(word) { puts "#{word} is awesome!" }
    
  • Never put a space between -> and the leading parenthesis for it's parameters

    # bad
    print_something = -> (something) { puts something }
    
    # good
    print_something = ->(something) { puts something }
    

Naming

  • Name identifiers in English.

  • Use snake_case for symbols, methods and variables.

    # bad
    :'some symbol'
    :SomeSymbol
    :someSymbol
    
    someVar = 5
    
    def someMethod
      ...
    end
    
    def SomeMethod
     ...
    end
    
    # good
    :some_symbol
    
    def some_method
      ...
    end
    
  • Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.)

    # bad
    class Someclass
      ...
    end
    
    class Some_Class
      ...
    end
    
    class SomeXml
      ...
    end
    
    # good
    class SomeClass
      ...
    end
    
    class SomeXML
      ...
    end
    
  • Use SCREAMING_SNAKE_CASE for other constants.

    # bad
    SomeConst = 5
    
    # good
    SOME_CONST = 5
    
  • The names of predicate methods (methods that return a boolean value) should end in a question mark. (i.e. Array#empty?).

  • 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.

    # bad - there is not matching 'safe' method
    class Person
      def update!
      end
    end
    
    # good
    class Person
      def update
      end
    end
    
    # good
    class Person
      def update!
      end
    
      def update
      end
    end
    
  • When using reduce with short blocks, name the arguments |a, e| (accumulator, element), or the singular form of the mapped variable.

  • When using map, name the argument |e| (element), or the singular form of the mapped variable.

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

    def +(other)
      # body omitted
    end
    
  • Prefer map over collect, reduce over inject, detect over find, select over find_all, and size over length.

  • 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.

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

Comments

  • Write comments sparingly, make code self-documenting whenever possible.
  • Write comments in English.
  • 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.
  • Avoid superfluous comments.

    # bad
    counter += 1 # increments counter by one
    
  • Keep existing comments up-to-date. An outdated comment is worse than no comment at all.

  • Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory.

Comment Annotations

  • Annotations should usually be written on the line immediately above the relevant code.
  • The annotation keyword inis 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 two spaces after the #.

    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
    
  • 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.

Classes & Modules

  • Use a consistent structure in your class definitions.

    class Person
      # extend and include go first
      extend SomeModule
      include AnotherModule
    
      # 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
    
      # private methods are grouped near the end
      private def some_private_method
      end
    
      private def another_private_method
      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.

    # bad
    class SomeClass
      def self.some_method
        # body omitted
      end
    
      def self.some_other_method
      end
    end
    
    # good
    module SomeClass
      module_function
    
      def some_method
        # body omitted
      end
    
      def some_other_method
      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
    
  • Use the attr family of functions to define trivial accessors or mutators.

    # 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
    
  • Avoid the usage of class (@@) variables due to their "nasty" behavior in inheritance.

    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"
    
  • Avoid class << self except when necessary, e.g. single accessors and aliased attributes.

    class TestClass
      # bad
      class << self
        def first_method
          # body omitted
        end
    
        def second_method_etc
          # body omitted
        end
      end
    
      # good
      class << self
        attr_accessor :per_page
        alias_method :nwo, :find_by_name_with_owner
      end
    
      def self.first_method
        # body omitted
      end
    
      def self.second_method_etc
        # body omitted
      end
    end
    

Private & Protected Methods

  • Avoid using protected whenever possible.

  • Assign proper visibility levels to methods (public or private) in accordance with their intended usage. Don't go off leaving everything public (which is the default).

  • For applications/gems with Ruby >= 2.1, use private def method_name.

    # good
    class SomeClass
      def public_method
        # ...
      end
    
      private def private_method
        # ...
      end
    
      private def another_private_method
        # ...
      end
    end
    
  • For applications with Ruby < 2.1 and gems still supporting Ruby < 2.1, use private :method_name or private, depending on the existing convention in place.

  • Using private :method_name, pass the method name to public, or private one line below the visibility controlled method.

    # ok
    class SomeClass
      def public_method
        # ...
      end
    
      def private_method
        # ...
      end
      private :private_method
    
      def another_private_method
        # ...
      end
      private :private_method
    end
    
  • For private blocks, indent the 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.

    # bad - private methods are indented too far
    class SomeClass
      def public_method
        # ...
      end
    
      private
    
        def private_method
          # ...
        end
    
        def another_private_method
          # ...
        end
    end
    
    # ok
    class SomeClass
      def public_method
        # ...
      end
    
      private
    
      def private_method
        # ...
      end
    
      def another_private_method
        # ...
      end
    end
    

Exceptions

  • Never 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.

    def foo
      begin
        fail
      ensure
        return 'very bad idea'
      end
    end
    
  • Use implicit begin blocks where possible.

    # 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).

    # 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.

    # 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.

    # bad - this catches all StandardError exceptions
    do_something rescue nil
    
  • Don't use exceptions for flow of control.

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

  • Favor error classes over exception classes.

  • Favor inheriting from StandardError over Exception when defining new errors/exceptions.

  • Basic errors should be defined on a single line using Class.new.

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

Collections

  • Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).

    # bad
    arr = Array.new
    hash = Hash.new
    
    # good
    arr = []
    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 this rule only to arrays with two or more elements.

    # bad
    STATES = ['draft', 'open', 'closed']
    
    # good
    STATES = %w(draft open closed)
    
  • Avoid the creation of huge gaps in arrays.

    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].

  • Prefer symbols instead of strings as hash keys.

    # 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.

  • Use the hash literal syntax when your hash keys are symbols.

    # bad
    hash = { :one => 1, :two => 2, :three => 3 }
    
    # good
    hash = { one: 1, two: 2, three: 3 }
    
  • Use fetch when dealing with hash keys that should be present.

    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)
    
  • Use fetch with second argument to use a default value

    batman = { name: 'Bruce Wayne', is_evil: false }
    
    # bad - if we just use || operator with falsy value we won't get the expected result
    batman[:is_evil] || true # => true
    
    # good - fetch work correctly with falsy values
    batman.fetch(:is_evil, true) # => false
    
  • Rely on the fact that as of Ruby 1.9 hashes are ordered.

Strings

  • Prefer string interpolation instead of string concatenation:

    # bad
    email_with_name = user.name + ' <' + user.email + '>'
    
    # good
    email_with_name = "#{user.name} <#{user.email}>"
    
  • Prefer double-quoted strings. Interpolation and escaped characters will always work without a delimiter change, and ' is a lot more common than " in string literals.

    # bad
    name = 'Bozhidar'
    
    # good
    name = "Bozhidar"
    
  • Don't leave out {} around instance and global variables being interpolated into a string.

    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 pass heredoc strings to methods. Use a temporary variable.

    # bad
    execute(<<-QUERY)
      UPDATE users SET username = "Bob" WHERE id=1;
      UPDATE users SET username = "Billy" WHERE id=2;
    QUERY
    
    # good
    query = <<-QUERY
      UPDATE users SET username = "Bob" WHERE id=1;
      UPDATE users SET username = "Billy" WHERE id=2;
    QUERY
    execute(query)
    

Regular Expressions

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

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

    /(first|second)/   # bad
    /(?:first|second)/ # good
    
  • Avoid using $1-9 as it can be hard to track what they contain. Named groups can be used instead.

    # bad
    /(regexp)/ =~ string
    ...
    process $1
    
    # good
    /(?<meaningful_var>regexp)/ =~ string
    ...
    process meaningful_var
    

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>)
    

Misc

  • 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
    
  • Avoid alias when alias_method will do.

  • 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 arguments 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.

Never Ever

  • Never use if x: ... - as of Ruby 1.9 it has been removed. Use the ternary operator instead.

  • Never use if x; .... Use the ternary operator instead.

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

  • Never use when x; .... See the previous rule.

  • Don't use ; to separate statements and expressions. As a corollary - use one expression per line. In general, don't use semicolons.

    # bad
    puts 'foobar'; # superfluous semicolon
    
    puts 'foo'; puts 'bar' # two expression on the same line
    
    # good
    puts 'foobar'
    
    puts 'foo'
    puts 'bar'
    
    puts 'foo', 'bar' # this applies to puts in particular
    
  • Never use for

  • Avoid using Perl-style special variables (like $0-9, $, etc. )

  • Never put a space between a method name and the opening parenthesis.

    # bad
    f (3 + 2) + 1
    
    # good
    f(3 + 2) + 1
    
  • Use sprintf instead of String#% method.

    # bad
    '%d %d' % [20, 10]
    # => '20 10'
    
    # good
    sprintf('%d %d', 20, 10)
    # => '20 10'
    
  • Use Array#join instead of Array#* with a string argument.

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