Role models are important.
-- Officer Alex J. Murphy / RoboCop
One thing has always bothered me as a Ruby developer - Python developers have a great programming style reference (PEP-8) and we never got an official guide, documenting Ruby coding style and best practices. And I do believe that style matters. I also believe that a great hacker community, such as Ruby has, should be quite capable of producing this coveted document.
This guide started its life as our internal company Ruby coding guidelines (written by yours truly). At some point I decided that the work I was doing might be interesting to members of the Ruby community in general and that the world had little need for another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.
Since the inception of the guide I've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.
By the way, if you're into Rails you might want to check out the complementary Ruby on Rails 3 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 that is 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".
The guide is still a work in progress - some rules are lacking examples, some rules don't have examples that illustrate them clearly enough. In due time these issues will be addressed - just keep them in mind for now.
You can generate a PDF or an HTML copy of this guide using Transmuter.
RuboCop is a code analyzer, based on this style guide.
Translations of the guide are available in the following languages:
- Source Code Layout
- Syntax
- Naming
- Comments
- Classes
- Exceptions
- Collections
- Strings
- Regular Expressions
- Percent Literals
- Metaprogramming
- Misc
- Tools
Nearly everybody is convinced that every style but their own is ugly and unreadable. Leave out the "but their own" and they're probably right...
-- Jerry Coffin (on indentation)
-
Use
UTF-8
as the source file encoding. -
Use two spaces per indentation level. No hard tabs.
# bad - four spaces def some_method do_something end # good def some_method do_something end
-
Use Unix-style line endings. (*BSD/Solaris/Linux/OSX users are covered by default, Windows users have to be extra careful.)
- If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:
$ git config --global core.autocrlf true
-
Don't use
;
to separate statements and expressions. As a corollary - use one expression per line.# 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
-
Prefer a single-line format for class definitions with no body.
# bad class FooError < StandardError end # okish class FooError < StandardError; end # good FooError = Class.new(StandardError)
-
Avoid single-line methods. Although they are somewhat popular in the wild, there are a few peculiarities about their definition syntax that make their use undesirable. At any rate - there should be no more than one expression in a single-line method.
# 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 exception, regarding operators, is the exponent operator:
# bad e = M * c ** 2 # good e = 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 acceptable options:
# 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 style and apply it consistently.
-
No spaces after
(
,[
or before]
,)
.some(arg).other [1, 2, 3].length
-
No space after
!
.# bad ! something # good !something
-
Indent
when
as deep ascase
. I know that many would disagree with this one, but it's the style established in both "The Ruby Programming Language" and "Programming Ruby".# bad case when song.name == 'Misty' puts 'Not again!' when song.duration > 120 puts 'Too long!' when Time.now.hour > 21 puts "It's too late" else song.play end # good case when song.name == 'Misty' puts 'Not again!' when song.duration > 120 puts 'Too long!' when Time.now.hour > 21 puts "It's too late" else song.play end
-
When assigning the result of a conditional expression to a variable, preserve the usual alignment of its branches.
# bad - pretty convoluted kind = case year when 1850..1889 then 'Blues' when 1890..1909 then 'Ragtime' when 1910..1929 then 'New Orleans Jazz' when 1930..1939 then 'Swing' when 1940..1950 then 'Bebop' else 'Jazz' end result = if some_cond calc_something else calc_something_else end # good - it's apparent what's going on kind = case year when 1850..1889 then 'Blues' when 1890..1909 then 'Ragtime' when 1910..1929 then 'New Orleans Jazz' when 1930..1939 then 'Swing' when 1940..1950 then 'Bebop' else 'Jazz' end result = if some_cond calc_something else calc_something_else end # good (and a bit more width efficient) kind = case year when 1850..1889 then 'Blues' when 1890..1909 then 'Ragtime' when 1910..1929 then 'New Orleans Jazz' when 1930..1939 then 'Swing' when 1940..1950 then 'Bebop' else 'Jazz' end result = if some_cond calc_something else calc_something_else end
-
Use empty lines between method definitions and also to break up a method into logical paragraphs internally.
def some_method data = initialize(options) data.manipulate! data.result end def some_method result end
-
Use spaces around the
=
operator when assigning default values to method parameters:# bad def some_method(arg1=:default, arg2=nil, arg3=[]) # do something... end # good def some_method(arg1 = :default, arg2 = nil, arg3 = []) # do something... end
While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).
-
Avoid line continuation
\
where not required. In practice, avoid using line continuations for anything but string concatenation.# bad result = 1 - \ 2 # good (but still ugly as hell) result = 1 \ - 2 long_string = 'First part of the long string' \ ' and second part of the long string'
-
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 the parameters of a method call if they span more than one line. When aligning parameters is not appropriate due to line-length constraints, single indent for the lines after the first is also acceptable.
# starting point (line is too long) def send_mail(source) Mailer.deliver(to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text) end # bad (double indent) def send_mail(source) Mailer.deliver( to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text) end # good def send_mail(source) Mailer.deliver(to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text) end # good (normal indent) def send_mail(source) Mailer.deliver( to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text ) end
-
Align the elements of array literals spanning multiple lines.
# bad - single indent menu_item = ["Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Baked beans", "Spam", "Spam", "Spam", "Spam", "Spam"] # good menu_item = [ "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Baked beans", "Spam", "Spam", "Spam", "Spam", "Spam" ] # good menu_item = ["Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Spam", "Baked beans", "Spam", "Spam", "Spam", "Spam", "Spam"]
-
Add underscores to large numeric literals to improve their readability.
# bad - how many 0s are there? num = 1000000 # good - much easier to parse for the human brain num = 1_000_000
-
Use RDoc and its conventions for API documentation. Don't put an empty line between the comment block and the
def
. -
Limit lines to 80 characters.
-
Avoid trailing whitespace.
-
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
-
Use
::
only to reference constants(this includes classes and modules) and constructors (likeArray()
orNokogiri::HTML()
). Never use::
for regular method invocation.# bad SomeClass::some_method some_object::some_method # good SomeClass.some_method some_object.some_method SomeModule::SomeClass::SOME_CONST SomeModule::SomeClass()
-
Use
def
with parentheses when there are 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
for
, unless you know exactly why. Most of the time iterators should be used instead.for
is implemented in terms ofeach
(so you're adding a level of indirection), but with a twist -for
doesn't introduce a new scope (unlikeeach
) and variables defined in its block will be visible outside it.arr = [1, 2, 3] # bad for elem in arr do puts elem end # note that elem is accessible outside of the for loop elem #=> 3 # good arr.each { |elem| puts elem } # elem is not accessible outside each's block elem #=> NameError: undefined local variable or method `elem'
-
Never use
then
for multi-lineif/unless
.# bad if some_condition then # body omitted end # good if some_condition # body omitted end
-
Always put the condition on the same line as the
if
/unless
in a multi-line conditional.# bad if some_condition do_something do_something_else end # good if some_condition do_something do_something_else end
-
Favor the ternary operator(
?:
) overif/then/else/end
constructs. It's more common and obviously more concise.# 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
-
Never use
if x: ...
- as of Ruby 1.9 it has been removed. Use the ternary operator instead.# bad result = if some_condition: something else something_else end # good result = some_condition ? something : something_else
-
Never use
if x; ...
. Use the ternary operator instead. -
Use
when x then ...
for one-line cases. The alternative syntaxwhen x: ...
has been removed as of Ruby 1.9. -
Never use
when x; ...
. See the previous rule. -
Use
!
instead ofnot
.# bad - braces are required because of op precedence x = (not something) # good x = !something
-
Avoid the use of
!!
.# bad x = 'test' # obscure nil check if !!x # body omitted end x = false # double negation is useless on booleans !!x # => false # good x = 'test' if !x.nil? # body omitted end
-
The
and
andor
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!
-
Avoid multi-line
?:
(the ternary operator); useif/unless
instead. -
Favor modifier
if/unless
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
-
Favor
unless
overif
for negative conditions (or control flow||
).# 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
-
Never use
unless
withelse
. 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/until
.# bad if (x > 10) # body omitted end # good if x > 10 # body omitted end
-
Never use
while/until condition do
for multi-linewhile/until
.# bad while x > 5 do # body omitted end until x > 5 do # body omitted end # good while x > 5 # body omitted end until x > 5 # body omitted end
-
Favor modifier
while/until
usage when you have a single-line body.# bad while some_condition do_something end # good do_something while some_condition
-
Favor
until
overwhile
for negative conditions.# bad do_something while !some_condition # good do_something until some_condition
-
Use
Kernel#loop
with break rather thanbegin/end/until
orbegin/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 the outer braces around an implicit options hash.
# bad user.set({ name: 'John', age: 45, permissions: { read: true } }) # good user.set(name: 'John', age: 45, permissions: { read: true })
-
Omit both the outer braces and parentheses for methods that are part of an internal DSL.
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.
# bad Kernel.exit!() 2.even?() fork() 'test'.upcase() # good Kernel.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 usedo...end
for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs). Avoiddo...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 }
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?
-
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
-
As a corollary, 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
-
Don't use the return value of
=
(an assignment) in conditional expressions unless the assignment is wrapped in parentheses. This is a fairly popular idiom among Rubyists that's sometimes referred to as safe assignment in condition.# 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 # good v = array.grep(/foo/) if v do_something(v) ... 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 befalse
.)# bad - would set enabled to true even if it was false enabled ||= true # good enabled = true if enabled.nil?
-
Avoid explicit use of the case equality operator
===
. As its name implies it is meant to be used implicitly bycase
expressions and outside of them it yields some pretty confusing code.# bad Array === something (1..100) === 7 /something/ === some_string # good something.is_a?(Array) (1..100).include?(7) some_string =~ /something/
-
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.# bad $:.unshift File.dirname(__FILE__) # good require 'English' $LOAD_PATH.unshift File.dirname(__FILE__)
-
Never put a space between a method name and the opening parenthesis.
# bad f (3 + 2) + 1 # good f(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)
. -
Always run the Ruby interpreter with the
-w
option so it will warn you if you forget either of the rules above! -
Use the new lambda literal syntax for single line body blocks. Use the
lambda
method for multi-line blocks.# bad l = lambda { |a, b| a + b } l.call(1, 2) # correct, but looks extremely awkward l = ->(a, b) do tmp = a * 7 tmp * b / 50 end # good l = ->(a, b) { a + b } l.call(1, 2) l = lambda do |a, b| tmp = a * 7 tmp * b / 50 end
-
Prefer
proc
overProc.new
.# bad p = Proc.new { |n| puts n } # good p = proc { |n| puts n }
-
Prefer
proc.call()
overproc[]
orproc.()
for both lambdas and procs.# bad - looks similar to Enumeration access l = ->(v) { puts v } l[1] # also bad - uncommon syntax l = ->(v) { puts v } l.(1) # good l = ->(v) { puts v } l.call(1)
-
Use
_
for unused block parameters.# bad result = hash.map { |k, v| v + 1 } # good result = hash.map { |_, v| v + 1 }
-
Use
$stdout/$stderr/$stdin
instead ofSTDOUT/STDERR/STDIN
.STDOUT/STDERR/STDIN
are constants, and while you can actually reassign (possibly to redirect some stream) constants in Ruby, you'll get an interpreter warning if you do so. -
Use
warn
instead of$stderr.puts
. Apart from being more concise and clear,warn
allows you to suppress warnings if you need to (by setting the warn level to 0 via-W0
). -
Favor the use of
sprintf
and its aliasformat
over the fairly crypticString#%
method.# bad '%d %d' % [20, 10] # => '20 10' # good sprintf('%d %d', 20, 10) # => '20 10' # good sprintf('%{first} %{second}', first: 20, second: 10) # => '20 10' format('%d %d', 20, 10) # => '20 10' # good format('%{first} %{second}', first: 20, second: 10) # => '20 10'
-
Favor the use of
Array#join
over the fairly crypticArray#*
with a string argument.# bad %w(one two three) * ', ' # => 'one, two, three' # good %w(one two three).join(', ') # => 'one, two, three'
-
Use
[*var]
orArray()
instead of explicitArray
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 or
Comparable#between?
instead of complex comparison logic when possible.# bad do_something if x >= 1000 && x <= 2000 # good do_something if (1000..2000).include?(x) # good do_something if x.between?(1000, 2000)
-
Favor the use of predicate methods to explicit comparisons with
==
. Numeric comparisons are OK.# bad if x % 2 == 0 end if x % 2 == 1 end if x == nil end # good if x.even? end if x.odd? end if x.nil? end if x.zero? end if x == 0 end
-
Avoid the use of
BEGIN
blocks. -
Never use
END
blocks. UseKernel#at_exit
instead.# bad END { puts 'Goodbye!' } # good at_exit { puts 'Goodbye!' }
-
Avoid the use of flip-flops.
-
Avoid use of nested conditionals for flow of control. Prefer a guard clause when you can assert invalid data. A guard clause is a conditional statement at the top of a function that bails out as soon as it can.
# bad def compute_thing(thing) if thing[:foo] update_with_bar(thing) if thing[:foo][:bar] partial_compute(thing) else re_compute(thing) end end end # good def compute_thing(thing) return unless thing[:foo] update_with_bar(thing[:foo]) return re_compute(thing) unless thing[:foo][:bar] partial_compute(thing) end
The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton
-
Name identifiers in English.
# bad - identifier using non-ascii characters заплата = 1_000 # bad - identifier is a Bulgarian word, written with Latin letters (instead of Cyrillic) zaplata = 1_000 # good salary = 1_000
-
Use
snake_case
for symbols, methods and variables.# 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?
). Methods that don't return a boolean, shouldn't end in a question mark. -
The names of potentially dangerous methods (i.e. methods that modify
self
or the arguments,exit!
(doesn't run the finalizers likeexit
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
-
Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.
class Array def flatten_once! res = [] each do |e| [*e].each { |f| res << f } end replace(res) end def flatten_once dup.flatten_once! end end
-
When using
reduce
with short blocks, name the arguments|a, e|
(accumulator, element). -
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
overcollect
,find
overdetect
,select
overfind_all
,reduce
overinject
andsize
overlength
. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use ofselect
is encouraged overfind_all
is that it goes together nicely withreject
and its name is pretty self-explanatory. -
Use
flat_map
instead ofmap
+flatten
. This does not apply for arrays with a depth greater than 2, i.e. ifusers.first.songs == ['a', ['b','c']]
, then usemap + flatten
rather thanflat_map
.flat_map
flattens the array by 1, whereasflatten
flattens it all the way.# bad all_songs = users.map(&:songs).flatten.uniq # good all_songs = users.flat_map(&:songs).uniq
-
Use
reverse_each
instead ofreverse.each
.reverse_each
doesn't do a new array allocation and that's a good thing.# bad array.reverse.each { ... } # good array.reverse_each { ... }
Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?" Improve the code and then document it to make it even clearer.
-- Steve McConnell
-
Write self-documenting code and ignore the rest of this section. Seriously!
-
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.
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 it self-explanatory. (Do or do not - there is no try. --Yoda)
-
Annotations should usually be written on the line immediately above the relevant code.
-
The annotation keyword is followed by a colon and a space, then a note describing the problem.
-
If multiple lines are required to describe the problem, subsequent lines should be indented 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.
-
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 # protected and private methods are grouped near the end protected def some_protected_method end private def some_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
overextend self
when you want to turn a module's instance methods into class methods.# bad module Utilities extend self def parse_something(string) # do stuff here end def other_utility_method(number, string) # do some more stuff end end # good module Utilities module_function def parse_something(string) # do stuff here end def other_utility_method(number, string) # do some more stuff end end
-
When designing class hierarchies make sure that they conform to the Liskov Substitution Principle.
-
Try to make your classes as [SOLID](http://en.wikipedia.org/wiki/SOLID_(object-oriented_design\)) as possible.
-
Always supply a proper
to_s
method for classes that represent domain objects.class Person attr_reader :first_name, :last_name def initialize(first_name, last_name) @first_name = first_name @last_name = last_name end def to_s "#{@first_name} #{@last_name}" end end
-
Use the
attr
family of functions to define trivial accessors or mutators.# 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 use of
attr
. Useattr_reader
andattr_accessor
instead.# bad - creates a single attribute accessor (deprecated in 1.9) attr :something, true attr :one, :two, :three # behaves as attr_reader # good attr_accessor :something attr_reader :one, :two, :three
-
Consider using
Struct.new
, which defines the trivial accessors, constructor and comparison operators for you.# 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 # better Person = Struct.new(:first_name, :last_name) do end
-
Don't extend a
Struct.new
- it already is a new class. Extending it introduces a superfluous class level and may also introduce weird errors if the file is required multiple times. -
Consider adding factory methods to provide additional sensible ways to create instances of a particular class.
class Person def self.create(options_hash) # body omitted end end
-
Prefer duck-typing over inheritance.
# bad class Animal # abstract method def speak end end # extend superclass class Duck < Animal def speak puts 'Quack! Quack' end end # extend superclass class Dog < Animal def speak puts 'Bau! Bau!' end end # good class Duck def speak puts 'Quack! Quack' end end class Dog def speak puts 'Bau! Bau!' end end
-
Avoid the usage of class (
@@
) variables due to their "nasty" behavior in inheritance.class Parent @@class_var = 'parent' def self.print_class_var puts @@class_var end end class Child < Parent @@class_var = 'child' end Parent.print_class_var # => will print "child"
As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.
-
Assign proper visibility levels to methods (
private
,protected
) in accordance with their intended usage. Don't go off leaving everythingpublic
(which is the default). After all we're coding in Ruby now, not in Python. -
Indent the
public
,protected
, andprivate
methods as much 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.class SomeClass def public_method # ... end private def private_method # ... end def another_private_method # ... end end
-
Use
def self.method
to define singleton methods. This makes the code easier to refactor since the class name is not repeated.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 end end
-
Signal exceptions using the
fail
method. Useraise
only when catching an exception and re-raising it (because here you're not failing, but explicitly and purposefully raising an exception).begin fail 'Oops' rescue => error raise if error.message != 'Oops' end
-
Don't specify
RuntimeError
explicitly in the two argument version offail/raise
.# bad fail RuntimeError, 'message' # good - signals a RuntimeError by default fail 'message'
-
Prefer supplying an exception class and a message as two separate arguments to
fail/raise
, instead of an exception instance.# bad fail SomeException.new('message') # Note that there is no way to do `fail SomeException.new('message'), backtrace`. # good fail SomeException, 'message' # Consistent with `fail SomeException, 'message', backtrace`.
-
Never return from an
ensure
block. If you explicitly return from a method inside anensure
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 exceptions of StandardError class and its descendant classes read_file rescue handle_error($!) # good - this catches only the exceptions of Errno::ENOENT class and its descendant classes def foo read_file rescue Errno::ENOENT => ex handle_error(ex) end
-
Don't use exceptions for flow of control.
# 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 toexit
, requiring you tokill -9
the process.# bad begin # calls to exit and kill signals will be caught (except kill -9) exit rescue Exception puts "you didn't really want to exit, right?" # exception handling end # good begin # a blind rescue rescues from StandardError, not Exception as many # programmers assume. rescue => e # exception handling end # also good begin # an exception occurs here rescue StandardError => e # exception handling end
-
Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from.
# bad begin # some code rescue Exception => e # some handling rescue StandardError => e # some handling end # good begin # some code rescue StandardError => e # some handling rescue Exception => e # some handling end
-
Release external resources obtained by your program in an ensure block.
f = File.open('testfile') begin # .. process rescue # .. handle error ensure f.close unless f.nil? end
-
Favor the use of exceptions for the standard library over introducing new exception classes.
-
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)
-
Prefer
%i
to the literal array syntax when you need an array of symbols(and you don't need to maintain Ruby 1.9 compatibility). Apply this rule only to arrays with two or more elements.# bad STATES = [:draft, :open, :closed] # good STATES = %i(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
orlast
over[0]
or[-1]
. -
Use
Set
instead ofArray
when dealing with unique elements.Set
implements a collection of unordered values with no duplicates. This is a hybrid ofArray
's intuitive inter-operation facilities andHash
's fast lookup. -
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
Hash#key?
instead ofHash#has_key?
andHash#value?
instead ofHash#has_value?
. As noted here by Matz, the longer forms are considered deprecated.# bad hash.has_key?(:test) hash.has_value?(value) # good hash.key?(:test) hash.value?(value)
-
Use
Hash#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)
-
Introduce default values for hash keys via
Hash#fetch
as opposed to using custom logic.batman = { name: 'Bruce Wayne', is_evil: false } # bad - if we just use || operator with falsy value we won't get the expected result batman[:is_evil] || true # => true # good - fetch work correctly with falsy values batman.fetch(:is_evil, true) # => false
-
Prefer the use of the block instead of the default value in
Hash#fetch
.batman = { name: 'Bruce Wayne' } # bad - if we use the default value, we eager evaluate it # so it can slow the program down if done multiple times batman.fetch(:powers, get_batman_powers) # get_batman_powers is an expensive call # good - blocks are lazy evaluated, so only triggered in case of KeyError exception batman.fetch(:powers) { get_batman_powers }
-
Rely on the fact that as of Ruby 1.9 hashes are ordered.
-
Never modify a collection while traversing it.
-
Prefer string interpolation instead of string concatenation:
# bad email_with_name = user.name + ' <' + user.email + '>' # good email_with_name = "#{user.name} <#{user.email}>"
-
Consider padding string interpolation code with space. It more clearly sets the code apart from the string.
"#{ user.last_name }, #{ user.first_name }"
-
Prefer single-quoted strings when you don't need string interpolation or special symbols such as
\t
,\n
,'
, etc.# bad name = "Bozhidar" # good name = 'Bozhidar'
-
Don't use the character literal syntax
?x
. Since Ruby 1.9 it's basically redundant -?x
would interpreted as'x'
(a string with a single character in it).# bad char = ?c # good char = 'c'
-
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}"
-
Avoid using
String#+
when you need to construct large data chunks. Instead, useString#<<
. Concatenation mutates the string instance in-place and is always faster thanString#+
, which creates a bunch of new string objects.# good and also fast html = '' html << '<h1>Page title</h1>' paragraphs.each do |paragraph| html << "<p>#{paragraph}</p>" end
-
When using heredocs for multi-line strings keep in mind the fact that they preserve leading whitespace. It's a good practice to employ some margin based on which to trim the excessive whitespace.
code = <<-END.gsub(/^\s+\|/, '') |def test | some_method | other_method |end END #=> "def test\n some_method\n other_method\nend\n"
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.
-- Jamie Zawinski
-
Don't use regular expressions if you just need plain text search in string:
string['text']
-
For simple constructions you can use regexp directly through string index.
match = string[/regexp/] # get content of matched regexp first_group = string[/text(grp)/, 1] # get content of captured group string[/text (grp)/, 1] = 'replace' # string => 'text replace'
-
Use non-capturing groups when you don't use captured result of parentheses.
/(first|second)/ # bad /(?:first|second)/ # good
-
Don't use the cryptic Perl-legacy variables denoting last regexp group matches (
$1
,$2
, etc). UseRegexp.last_match[n]
instead./(regexp)/ =~ string ... # bad process $1 # good process Regexp.last_match[1]
-
Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead.
# bad /(regexp)/ =~ string ... process Regexp.last_match[1] # good /(?<meaningful_var>regexp)/ =~ string ... process meaningful_var
-
Character classes have only a few special characters you should care about:
^
,-
,\
,]
, so don't escape.
or brackets in[]
. -
Be careful with
^
and$
as they match start/end of line, not string endings. If you want to match the whole string use:\A
and\z
(not to be confused with\Z
which is the equivalent of/\n?\z/
).string = "some injection\nusername" string[/^username$/] # matches string[/\Ausername\z/] # don't match
-
Use
x
modifier for complex regexps. This makes them more readable and you can add some useful comments. Just be careful as spaces are ignored.regexp = %r{ start # some text \s # white space char (group) # first group (?:alt1|alt2) # some alternation end }x
-
For complex replacements
sub
/gsub
can be used with block or hash.
-
Use
%()
(it's a shorthand for%Q
) for single-line strings which require both interpolation and embedded double-quotes. For multi-line strings, prefer heredocs.# bad (no interpolation needed) %(<div class="text">Some text</div>) # should be '<div class="text">Some text</div>' # bad (no double-quotes) %(This is #{quality} style) # should be "This is #{quality} style" # bad (multiple lines) %(<div>\n<span class="big">#{exclamation}</span>\n</div>) # should be a heredoc. # good (requires interpolation, has quotes, single line) %(<tr><td class="name">#{name}</td>)
-
Avoid
%q
unless you have a string with both'
and"
in it. Regular string literals are more readable and should be preferred unless a lot of characters would have to be escaped in them.# bad name = %q(Bruce Wayne) time = %q(8 o'clock) question = %q("What did you say?") # good name = 'Bruce Wayne' time = "8 o'clock" question = '"What did you say?"'
-
Use
%r
only for regular expressions matching more than one '/' character.# bad %r(\s+) # still bad %r(^/(.*)$) # should be /^\/(.*)$/ # good %r(^/blog/2011/(.*)$)
-
Avoid the use of
%x
unless you're going to invoke a command with backquotes in it(which is rather unlikely).# bad date = %x(date) # good date = `date` echo = %x(echo `date`)
-
Avoid the use of
%s
. It seems that the community has decided:"some string"
is the preferred way to created a symbol with spaces in it. -
Prefer
()
as delimiters for all%
literals, except%r
. Since braces often appear inside regular expressions in many scenarios a less common character like{
might be a better choice for a delimiter, depending on the regexp's content.# bad %w[one two three] %q{"Test's king!", John said.} # good %w(one two three) %q("Test's king!", John said.)
-
Avoid needless metaprogramming.
-
Do not mess around in core classes when writing libraries. (Do not monkey-patch them.)
-
The block form of
class_eval
is preferable to the string-interpolated form.-
when you use the string-interpolated form, always supply
__FILE__
and__LINE__
, so that your backtraces make sense:class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
-
define_method
is preferable toclass_eval{ def ... }
-
-
When using
class_eval
(or othereval
) with string interpolation, add a comment block showing its appearance if interpolated (a practice I learned from the Rails code):# from activesupport/lib/active_support/core_ext/string/output_safety.rb UNSAFE_STRING_METHODS.each do |unsafe_method| if 'String'.respond_to?(unsafe_method) class_eval <<-EOT, __FILE__, __LINE__ + 1 def #{unsafe_method}(*args, &block) # def capitalize(*args, &block) to_str.#{unsafe_method}(*args, &block) # to_str.capitalize(*args, &block) end # end def #{unsafe_method}!(*args) # def capitalize!(*args) @dirty = true # @dirty = true super # super end # end EOT end end
-
Avoid using
method_missing
for metaprogramming because backtraces become messy, the behavior is not listed in#methods
, and misspelled method calls might silently work, e.g.nukes.launch_state = false
. Consider using delegation, proxy, ordefine_method
instead. If you must usemethod_missing
:-
Be sure to also define
respond_to_missing?
-
Only catch methods with a well-defined prefix, such as
find_by_*
-- make your code as assertive as possible. -
Call
super
at the end of your statement -
Delegate to assertive, non-magical methods:
# bad def method_missing?(meth, *args, &block) if /^find_by_(?<prop>.*)/ =~ meth # ... lots of code to do a find_by else super end end # good def method_missing?(meth, *args, &block) if /^find_by_(?<prop>.*)/ =~ meth find_by(prop, *args, &block) else super end end # best of all, though, would to define_method as each findable attribute is declared
-
-
Write
ruby -w
safe code. -
Avoid hashes as optional parameters. Does the method do too much? (Object initializers are exceptions for this rule).
-
Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC.
-
Avoid parameter lists longer than three or four parameters.
-
If you really need "global" methods, add them to Kernel and make them private.
-
Use module instance variables instead of global variables.
# bad $foo_bar = 1 #good module Foo class << self attr_accessor :bar end end Foo.bar = 1
-
Avoid
alias
whenalias_method
will do. -
Use
OptionParser
for parsing complex command line options andruby -s
for trivial command line options. -
Prefer
Time.now
overTime.new
when retrieving the current system time. -
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.
Here's some tools to help you automatically check Ruby code against this guide.
RuboCop is a Ruby code style checker based on this style guide. RuboCop already covers a significant portion of the Guide, supports both MRI 1.9 and MRI 2.0 and has good Emacs integration.
RubyMine's code inspections are partially based on this guide.
Nothing written in this guide is set in stone. It's my desire to work together with everyone interested in Ruby coding style, so that we could ultimately create a resource that will be beneficial to the entire Ruby community.
Feel free to open tickets or send pull requests with improvements. Thanks in advance for your help!
This work is licensed under a Creative Commons Attribution 3.0 Unported License
A community-driven style guide is of little use to a community that doesn't know about its existence. Tweet about the guide, share it with your friends and colleagues. Every comment, suggestion or opinion we get makes the guide just a little bit better. And we want to have the best possible guide, don't we?
Cheers,
Bozhidar