SportsEngine Style Guide
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Ruby

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 single-quoted strings.

    # 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'