- Source Code Layout
- Comments
- Naming
- General Syntax
- Strings
- Conditionals
- Collections
- Iteration
- Methods
- Exceptions
- Regular Expressions
- Blocks / Procs
- Classes
- Misc
- Rails
- References
##1. Source Code Layout
-
Use
UTF-8
as the source file encoding. -
Use two spaces per indentation level, no tabs.
-
Leave no trailing whitespace of any kind.
-
Do not leave a blank line at the bottom of the file.
-
Use Unix-style line endings. (*BSD/Solaris/Linux/OSX users are covered by default, Windows users have to be extra careful.)
-
Keep lines 94 characters wide or less.
##2. Comments
-
Write self-documenting code. If feel you need a comment, refactor the code until a comment feels like overkill. Then, ignore the rest of this section.
-
Comments longer than a word are capitalized and use punctuation.
-
Avoid superfluous comments.
# bad counter += 1 # increments counter by one
-
Keep existing comments up-to-date. An outdated is worse than no comment at all.
-
Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory.
-
Avoid code banners. Your class is probably too big if you need them. Refactor!
################################################ # Code banners are a code smell ################################################
-
Parameter explanations, examples, return descriptions, etc., are often overkill, but you should consider adding them to public API methods. If you do add them, follow tomdoc's conventions.
-
Write inline comments like this:
# This is a description of the line. @pages.each { |p| puts p.name }
-
Write comments for methods, classes, modules, etc., like this:
# Print a log line to STDOUT. You can customize the output by specifying # a block. # # msgs - Zero or more String messages that will be printed to the log # separated by spaces. # block - An optional block that can be used to customize the date format. # If it is present, it will be sent a Time object representing # the current time. Your block should return a String version of # the time, formatted however you please. # # Examples # # log("An error occurred.") # # log("No such file", "/var/log/server.log") do |time| # time.strftime("%Y-%m-%d %H:%M:%S") # end # # Returns nothing. # def log(*msgs, &block) ... end
##3. Naming
-
Use
snake_case
for methods and variables. -
Use
CamelCase
for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.) -
Use
SCREAMING_SNAKE_CASE
for other constants. -
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 likeexit
does), etc.) should end with an exclamation mark if and only 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 defining binary operators, name the argument
other
.def +(other) # body omitted end
##4. General Syntax
-
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 is when using the exponent operator:
# bad e = M * c ** 2 # good e = M * c**2
-
No spaces after
(
,[
or before]
,)
.some(arg).other [1, 2, 3].length
##5. 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 when you don't need string interpolation or special symbols such as
\t
,\n
,'
, etc.# bad name = "Bozhidar" # good name = 'Bozhidar'
-
Don't use
{}
around instance 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 def to_s "#{@first_name} #{@last_name}" end # good def to_s "#@first_name #@last_name" end end
-
Use
%()
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
and%Q
. -
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
##6. Conditionals
-
Indent
when
as deep ascase
.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
when x then ...
for one-line conditions in case blocks. -
Never use
then
for multi-lineif/unless
.# bad if some_condition then # body omitted end # good if some_condition # body omitted end
-
Favour 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
-
Avoid multi-line
?:
(the ternary operator), useif/unless
instead. -
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; ...
. Use the ternary operator instead. -
Never use
when x; ...
. See the previous rule. -
Use
&&/||
for boolean expressions,and/or
for control flow. (Rule of thumb: If you have to use outer parentheses, you are using the wrong operators.)# boolean expression if some_condition && some_other_condition do_something end # control flow document.saved? or document.save!
-
Favour modifier
if/unless
usage when you have a single-line body.# bad if some_condition do_something end # good do_something if some_condition
-
Favour
unless
overif
for negative conditions (or control flowor
).# bad do_something if !some_condition # good do_something unless some_condition # another good option some_condition or 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
, unless the condition contains an assignment (see "Using the return value of=
" below).# bad if (x > 10) # body omitted end # good if x > 10 # body omitted end # ok if (x = self.next_value) # body omitted end
-
Favour
!
overnot
. The latter binds more loosely, and can lead to confusing results.
##7. 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 single-word strings.# bad STATES = ['draft', 'open', 'closed'] # good STATES = %w(draft open closed)
-
Use parentheses are the delimeters for
%w
.# bad STATES = %w[draft open closed] # good STATES = %w(draft open closed)
-
Avoid
%W
. -
Avoid the creation of huge gaps in arrays.
arr = [] arr[100] = 1 # now you have an array with lots of nils
-
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. -
Use 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 new Ruby 1.9 has syntax whenever possible. For cases in which the hash keys cannot be symbolized, use the old syntax.
# good hash = { one: 1, two: 2, three: 3 } # deprecated hash = { :one => 1, :two => 2, :three => 3 }
-
Rely on the fact that hashes in 1.9 are ordered.
-
Leave a single space padding inside the braces of a hash.
# bad hash = {one: 1, two: 2} # good hash = { one: 1, two: 2 }
-
Leave no padding inside the brackets of an array.
# bad array = [ 1, 2, 3 ] # good array = [1, 2, 3]
-
Use a single line for arrays and hashes if they will fit.
-
Format multiline hashes and arrays by indenting two-spaces.
hash = { name: 'peter', professional: 'teacher', favourite_color: 'green' } array = [ 'Happy Sauce', 'Awesome people eating computers' ]
-
You may optionally align hash values if it improves readability. Especially when there are many keys.
hash = { name: 'peter', professional: 'teacher', favourite_color: 'green' }
-
Prefer
size
overlength
for getting the number of elements.
##8. Iteration
-
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 # good arr.each { |elem| puts elem }
-
Favour modifier
while/until
usage when you have a single-line body.# bad while some_condition do_something end # good do_something while some_condition
-
Favour
until
overwhile
for negative conditions.# bad do_something while !some_condition # good do_something until some_condition
-
Never modify a collection while traversing it.
-
Know the iterators provided to you by Hash, Array, and enumerable. Don't re-invent the wheel.
-
Prefer
map
overcollect
,find
overdetect
,select
overfind_all
,reduce
overinject
. -
When using
reduce
with short blocks, name the arguments|a, e|
(accumulator, element).
##9. Methods
-
Use empty lines between
def
s 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
-
Indent the parameters of a method call if they span over multiple lines.
# 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 Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text) # good Mailer.deliver( to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text ) # also good create( :invitation, email: 'bob@example.com', role: :author )
-
Use
def
with parentheses when there are arguments. Omit the parentheses when the method doesn't accept any arguments.def some_method # body omitted end def some_method_with_arguments(arg1, arg2) # body omitted end
-
Omit parentheses around parameters for methods that are part of an internal DSL (e.g. Rake, Rails, RSpec), methods that are with "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)
-
Avoid
return
where not required.# bad def some_method(some_arr) return some_arr.size end # good def some_method(some_arr) some_arr.size 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
-
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)
. -
If the last parameter is a hash, don't use curly brackets around the arguments.
# bad do_something({ param1: value1, param2: value2 }) # good do_something( param1: value1, param2: value2 )
##10. Exceptions
-
Use
e
as the rescued variable:rescue StandardError => e
-
Signal exceptions using the
fail
keyword. 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 => e raise if e.message != 'Oops' end
-
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 when 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.
# bad begin # an exception occurs here rescue SomeError # the rescue clause does absolutely nothing end # bad 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 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
-
Favour the use of exceptions for the standard library over introducing new exception classes.
##11. Regular Expressions
-
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 parenthesis.
/(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 $1 # good /(?<meaningful_var>regexp)/ =~ string ... process meaningful_var
-
Character classes have only few special characters you should care about:
^
,-
,\
,]
, so don't escape.
or brackets in[]
. -
Be careful with
^
and$
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$/] # matches string[/\Ausername\z/] # don't match
-
Use
%r
only for regular expressions matching more than one '/' character.# bad %r(\s+) # still bad %r(^/(.*)$) # should be /^\/(.*)$/ # good %r(^/blog/2011/(.*)$)
-
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.
##12. Blocks / Procs
-
Use
{...}
overdo...end
for single-line blocks.# good names.each { |name| puts name } # bad names.each do |name| puts name end
-
Use
{...}
overdo...end
when chaining.# good names.select { |name| name.start_with?('S') }.map { |name| name.upcase } # good expect { page.publish }.to raise_error(StandardError) # bad names.select do |name| name.start_with?('S') end.map { |name| name.upcase }
-
Use the old lambda syntax over the new literal syntax. NOTE: We prefer the new syntax, but are staying with the old for consistency with the existing codebase.
# bad lambda = ->(a, b) { a + b } lambda.(1, 2) # good lambda = lambda { |a, b| a + b } lambda.call(1, 2)
-
Use
_
for unused block parameters.# bad result = hash.map { |k, v| v + 1 } # good result = hash.map { |_, v| v + 1 }
##13. Classes
-
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 # 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 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"
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). -
Prefer
private
visibility overprotected
unless you truly know you need the latter. -
Indent
private
andprotected
methods.class SomeClass def public_method # ... end private def private_method # ... end end
-
Order methods in your classes by visibility:
public
, thenprotected
, andprivate
at the bottom. -
Order class methods before instance methods.
-
Use
def self.method
to define singleton methods. This makes the methods more resistant to refactoring changes.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
##14. 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 have to, add "global" methods to Kernel and make them private.
-
Use class instance variables instead of global variables.
#bad $foo_bar = 1 #good class Foo class << self attr_accessor :bar end end Foo.bar = 1
-
Avoid
alias
whenalias_method
will do. -
Avoid needless metaprogramming.
-
Do not mutate arguments unless that is the purpose of the method.
-
Avoid more than three levels of block nesting.
-
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
-
Using the return value of
=
(an assignment) is ok, but surround the assignment with parenthesis.# good - shows intended use of assignment if (v = array.grep(/foo/)) ... # bad if v = array.grep(/foo/) ... # also good - shows intended use of assignment and has correct precedence. if (v = self.next_value) == 'hello' ...
-
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 using Perl-style special variables (like
$0-9
, `$``, etc. ). They are quite cryptic and their use in anything but one-liner scripts is discouraged. -
Prefer
()
as delimiters for all%
literals.
##15. Rails
See the examples in model.rb
, model_spec.rb
, factory.rb
, and view.html.erb
for canonical examples.
##16. References
Read these books and guides:
-
Eloquent Ruby
-
The Well-grounded Rubyist
-
Rails guides
-
Clean Code (Robert C. Martin)