Prelude
If you're into Rails you might want to check out the complementary. Ruby on Rails 3 & 4 Style Guide.
The Ruby Style Guide
Be consistent.
Table of Contents
- Source Code Layout
- Syntax
- Naming
- Comments
- Classes
- Exceptions
- Collections
- Strings
- Regular Expressions
- Percent Literals
- Metaprogramming
- Misc
- Tools
Source Code Layout
-
Use
UTF-8
as the source file encoding. -
Use two spaces per indentation level (aka soft tabs). No hard tabs.
# bad - four spaces def some_method do_something end # good def some_method do_something end
-
Limit lines to 80 characters.
-
Avoid trailing whitespace.
-
End each file with a newline.
-
Use Unix-style line endings. (*BSD/Solaris/Linux/OS X 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 expressions on the same line # good puts 'foobar' puts 'foo' puts 'bar' puts 'foo', 'bar' # this applies to puts in particular
-
Prefer a single-line format for class definitions with no body.
# 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 ; makes it kind of hard to read def some_method() body end # good def some_method body end
One exception to the rule are empty-body methods.
# good def no_op; end
-
Use spaces around operators, after commas, colons and semicolons, 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, 3].each { |e| puts e } class FooError < StandardError; end
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, no space after and before{
and}
, respectively.# bad - space after { and before } { one: 1, two: 2 } # good - no space after { and before } {one: 1, two: 2}
As far as embedded expressions go, spaces before and after are unacceptable
# good - no spaces "string#{expr}" # bad - spaces "string#{ expr }"
-
No spaces after
(
,[
or before]
,)
.some(arg).other [1, 2, 3].size
-
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 # bad - whitespace isn't free when you only have 80 characters. 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.
# bad def some_method data = initialize(options) data.manipulate! data.result end def some_method result end # good def some_method data = initialize(options) data.manipulate! data.result end def some_method result end
-
Avoid comma after the last parameter in a method call, especially when the parameters are not on separate lines.
# bad - easier to move/add/remove parameters, but still not preferred some_method( size, count, color, ) # bad some_method(size, count, color, ) # good some_method(size, count, color)
-
Use spaces around the
=
operator when assigning default values to method parameters:# bad def some_method(arg1=:default, arg2=nil, arg3=[]) # do something... end # good def some_method(arg1 = :default, arg2 = nil, arg3 = []) # do something... end
While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).
-
Avoid line continuation
\
where not required. In practice, avoid using line continuations for anything but string concatenation.# 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: '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 # bad - wastes whitespace def send_mail(source) Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text) end # good (normal indent) def send_mail(source) Mailer.deliver( to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text ) end
-
Align the elements of array literals spanning multiple lines.
# bad - brackets/parentheses should be on separate line menu_item = ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam'] # bad 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
-
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
Syntax
-
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 # While defining methods using the constant syntax isn't best practice, they # exist, this is the best practice for calling them. 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 Enumerable 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. -
Leverage the fact that
if
andcase
are expressions which return a result.# bad if condition result = x else result = y end # good result = if condition x else y end
-
Use
when x then ...
for one-line cases. The alternative syntaxwhen x: ...
has been removed as of Ruby 1.9. -
Never use
when x; ...
. See the previous rule.# bad case when x; y end # good case when x then y end
-
Use
!
instead ofnot
.# bad - braces are required because of op precedence x = (not something) # good x = !something
-
Avoid the use of
!!
. Exceptions are for referencing large objects that would stick around longer than necessary.# bad x = 'test' # obscure nil check if !!x # body omitted end x = false # double negation is useless when you know the object is a boolean !!x # => false # good x = 'test' if x # body omitted end
-
The
and
andor
keywords are banned. It's just not worth it. Always use&&
and||
instead. Use parentheses rather than depend on binding differences.# 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
-
Avoid modifier
if/unless
usage at the end of a non-trivial multi-line block.# bad 10.times do # multi-line body omitted end if some_condition # good if some_condition 10.times do # multi-line body omitted end end
-
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
-
Always write the positive case or 'happy path' first. Prefer to not use
unless
withelse
.# bad unless success? puts 'failure' else puts 'success' end if failure? puts 'failure' else puts 'success' end # good if success? puts 'success' else puts 'failure' end # less good, but reasonable if there is no reasonable means to determine the positive case. # Prefer unless condition over ! condition unless failure? 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
instead ofwhile/until
when you need an infinite loop.# bad while true do_something end until false do_something end # good loop do do_something end
-
Use
Kernel#loop
withbreak
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 "method definitions" (e.g. in Rakefiles and certain DSLs).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 }
-
Always use an explicit block argument literal. Beware of the performance impact, though, as the block gets converted to a Proc.
require 'tempfile' # bad def with_tmp_dir Dir.mktmpdir do |tmp_dir| Dir.chdir(tmp_dir) { |dir| yield dir } # block just passes arguments end end # good def with_tmp_dir(&block) Dir.mktmpdir do |tmp_dir| Dir.chdir(tmp_dir, &block) end end with_tmp_dir do |dir| puts "dir is accessible as a parameter and pwd is set: #{dir}" end
-
Avoid
return
where not required for flow of control.# 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.# 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 # bad def do_something(options = {}) unless options[:when] == :later output(self.options[:message]) end end # ok def initialize(options) self.options = options # both options and self.options are equivalent here 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.# bad (+ a warning) if v = array.grep(/foo/) do_something(v) ... end # bad (MRI would still complain, but RuboCop won't) if (v = array.grep(/foo/)) do_something(v) ... end # bad (MRI doesn't explain) if (v = array.grep(/foo/)).length.eq(3) do_something(v) ... end # good v = array.grep(/foo/) if v do_something(v) ... end
-
Use shorthand self assignment operators whenever applicable.
# bad x = x + y x = x * y x = x**y x = x / y x = x || y x = x && y # good x += y x *= y x **= y x /= y x ||= y x &&= y
-
Use
||=
to initialize variables only if they're not already initialized.# bad name = name ? name : 'Bozhidar' # bad name = 'Bozhidar' unless name # good - set name to Bozhidar, only if it's nil or false name ||= 'Bozhidar'
-
Don't use
||=
to initialize boolean variables. (Consider what would happen if the current value happened to befalse
.)# bad - would set enabled to true even if it was false enabled ||= true # good enabled = true if enabled.nil?
-
Use
&&=
to preprocess variables that may or may not exist. Using&&=
will change the value only if it exists, removing the need to check its existence withif
.# bad something = something ? nil : something.downcase # bad something = something.downcase if something # bad something = something && something.downcase # might be reasonable depending on length of method call if something something = something.downcase end # good something &&= something.downcase
-
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.
# ok l = lambda { |a, b| a + b } l.call(1, 2) # better l = ->(a, b) { a + b } l.call(1, 2)
-
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)
-
Prefix with
_
unused block parameters and local variables. It's also acceptable to use just_
(although it's a bit less descriptive). This convention is recognized by the Ruby interpreter and tools like RuboCop and will suppress their unused variable warnings.# bad result = hash.map { |k, v| v + 1 } def something(x) unused_var, used_var = something_else(x) # ... end # good result = hash.map { |_k, v| v + 1 } def something(x) _unused_var, used_var = something_else(x) # ... end # good result = hash.map { |_, v| v + 1 } def something(x) _, used_var = something_else(x) # ... end
-
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' # good 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 # ok if x == 0 end # good if x.even? end if x.odd? end if x.nil? end if x.zero? end
-
Don't do explicit non-
nil
checks unless you're dealing with boolean values.# bad do_something if !something.nil? do_something if something != nil # good do_something if something # good - dealing with a boolean def value_set? !@some_boolean.nil? end
-
Avoid the use of
BEGIN
blocks. -
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
Prefer
next
in loops as a guard clause instead of conditional blocks.# bad [0, 1, 2, 3].each do |item| if item > 1 puts item end end # good [0, 1, 2, 3].each do |item| next unless item > 1 puts item end
Naming
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. Note: Ruby itself violates this.# 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
snake_case
for naming files, e.g.hello_world.rb
. -
Use
snake_case
for naming directories, e.g.lib/hello_world/hello_world.rb
. -
Aim to have just a single class/module per source file. Name the file name as the class/module, but replacing CamelCase with snake_case.
-
Use
SCREAMING_SNAKE_CASE
for other constants.# bad SomeConst = 5 # good SOME_CONST = 5
-
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 no matching 'safe' method class Person def update! end end # good class Person def update end end # good class Person def update! end def update end end
-
Prefer
map
overcollect
,detect
overfind
,select
overfind_all
,reduce
overinject
. 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. -
Don't use
count
as a substitute forsize
. ForEnumerable
objects other thanArray
it will iterate the entire collection in order to determine its size.# bad some_hash.count # good some_hash.size
-
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 { ... }
Classes & Modules
-
Use a consistent structure in your class definitions.
class Person # constants that may be overridden by modules via prepend SOME_CONSTANT = 20 # extend and include go first prepend SomeModule extend AnotherModule include SomeOtherModule # constants are next SOME_CONSTANT = 20 # inner public class CustomErrorKlass = Class.new(StandardError) # 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 def private_inner_class Class.new(StandardError) end end
-
Don't nest multi line classes within classes. Try to have such nested classes each in their own file in a folder named like the containing class.
# bad # foo.rb class Foo class Bar # 30 methods inside end class Car # 20 methods inside end # 30 methods inside end # good # foo.rb class Foo # 30 methods inside end # foo/bar.rb class Foo class Bar # 30 methods inside end end # foo/car.rb class Foo class Car # 20 methods inside end end
-
Prefer modules to classes with only class methods. Classes should be used only when it makes sense to create instances out of them.
# 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
-
Avoid the usage of class (
@@
) variables due to their 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
protected
only if you actually need sibling instances to access the protected method -
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 end
Exceptions
-
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
-
Don't suppress exceptions unless you can actually handle the problem.
# 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
Collections
-
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 comma after the last item of an
Array
orHash
literal when the items are not on separate lines.# bad VALUES = [1001, 2020, 3333, ] # good VALUES = [1001, 2020, 3333]
-
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 }
-
Use the Ruby 1.9 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 }
-
Don't mix the Ruby 1.9 hash syntax with hash rockets in the same hash literal. When you've got keys that are not symbols stick to the hash rockets syntax.
# bad { a: 1, 'b' => 2 } # good { :a => 1, 'b' => 2 }
-
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
-
Use
Hash#values_at
when you need to retrieve several values consecutively from a hash.# bad email = data['email'] nickname = data['nickname'] # good email, username = data.values_at('email', 'nickname')
-
Be aware of the fact that as of Ruby 1.9 hashes are ordered and do not re-order.
-
Prefer not to modify a collection while traversing it.
Strings
-
Prefer string interpolation and string formatting instead of string concatenation:
# bad email_with_name = user.name + ' <' + user.email + '>' # good email_with_name = "#{user.name} <#{user.email}>" # good email_with_name = format('%s <%s>', user.name, user.email)
-
Adopt a consistent string literal quoting style. There are two popular styles in the Ruby community, both of which are considered good - single quotes by default (Option A) and double quotes by default (Option B).
-
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 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 = #{$global}"
-
Avoid using
String#+
when you need to construct large data chunks. Instead, useString#<<
. Concatenation mutates the string instance in-place and is always faster thanString#+
, which creates a bunch of new string objects.# good and also fast html = '' html << '<h1>Page title</h1>' paragraphs.each do |paragraph| html << "<p>#{paragraph}</p>" end
Regular Expressions
-
Use non-capturing groups when you don't use captured result of parentheses.
/(first|second)/ # bad /(?:first|second)/ # good
-
Character classes have only a few special characters you should care about:
^
,-
,\
,]
, so don't escape.
or brackets in[]
. -
Be careful with
^
and$
as they match start/end of line, not string endings. If you want to match the whole string use:\A
and\z
(not to be confused with\Z
which is the equivalent of/\n?\z/
).string = "some injection\nusername" string[/^username$/] # matches string[/\Ausername\z/] # doesn't match
-
For complex replacements
sub
/gsub
can be used with block or hash.
Percent Literals
-
Prefer
%r
for regular expressions.# bad /(\s+)/ # good %r|(\s+)|
-
Prefer the the use of
%s
. It seems that the community has decided:"some string"
is the preferred way to create a symbol with spaces in it. -
Prefer
|
as delimiters for all%
literals.# bad %w[one two three] %q{"Test's king!", John said.} # good %w|one two three| %q|"Test's king!", John said.|
Metaprogramming
-
Avoid needless metaprogramming.
-
Do not use string evaluation for metaprogramming! Use methods like
class_exec
,define_method
, etc. to dynamically create dynamically named methods, anonymous modules, etc.
Misc
-
Write
ruby -w
safe code. -
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.
-
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.
This work is licensed under a Creative Commons Attribution 3.0 Unported License
Original by Bozhidar