RubyMotion has some particular styling needs that don't translate perfectly from
either of its parents, Ruby and Objective-C. Some are immediately obvious, like
the class between methods_with_underscores in ruby, and methodsWithCapitals in
Objective-C. Some are subtler, like do we prefer new/initialize() or alloc/init*?
The RubyMotion community so far seems to skew ruby-oriented, so this document is directly
forked from "Ruby's", and conventions
will tend to lean in that direction.
This RubyMotion style guide recommends best practices so that real-world RubyMotion programmers can write code that can be maintained by other real-world RubyMotion 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.
From here on out, the guide will use "Ruby" and "RubyMotion" interchangeably, unless otherwise noted.
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:
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
Indent when
as deep as case
. I know that many would disagree
with this one, but it's the style established in both "The Ruby
Programming Language" and "Programming Ruby".
case
when song.name == 'Misty'
puts 'Not again!'
when song.duration > 120
puts 'Too long!'
when Time.now.hour > 21
puts "It's too late"
else
song.play
end
kind = case year
when 1850..1889 then 'Blues'
when 1890..1909 then 'Ragtime'
when 1910..1929 then 'New Orleans Jazz'
when 1930..1939 then 'Swing'
when 1940..1950 then 'Bebop'
else 'Jazz'
end
Use empty lines between 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
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 at all.
# bad
result = 1 - \
2
# good (but still ugly as hell)
result = 1 \
- 2
When continuing a chained method invocation on another line keep the .
on the second line.
# bad - need to consult first line to understand second line
one.two.three.
four
# good - it's immediately clear what's going on the second line
one.two.three
.four
Align 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
# good
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
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). Never use ::
for method invocation.
# bad
SomeClass::some_method
some_object::some_method
# good
SomeClass.some_method
some_object.some_method
SomeModule::SomeClass::SOME_CONST
Use def
with parentheses when there are arguments. Omit the
parentheses when the method doesn't accept any arguments.
# bad
def some_method()
# body omitted
end
# good
def some_method
# body omitted
end
# bad
def some_method_with_arguments arg1, arg2
# body omitted
end
# good
def some_method_with_arguments(arg1, arg2)
# body omitted
end
Never use for
, unless you know exactly why. Most of the time iterators
should be used instead. for
is implemented in terms of each
(so
you're adding a level of indirection), but with a twist - for
doesn't introduce a new scope (unlike each
) 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 }
Never use then
for multi-line if/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(?:
) over if/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 syntax
when x: ...
has been removed as of Ruby 1.9.
Never use when x; ...
. See the previous rule.
Use !
instead of not
.
# bad - braces are required because of op precedence
x = (not something)
# good
x = !something
The and
and or
keywords are banned. It's just not worth
it. Always use &&
and ||
instead.
# bad
# boolean expression
if some_condition and some_other_condition
do_something
end
# control flow
document.saved? or document.save!
# good
# boolean expression
if some_condition && some_other_condition
do_something
end
# control flow
document.saved? || document.save!
Avoid multi-line ?:
(the ternary operator); use if/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
over if
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
with else
. Rewrite these with the positive case first.
# bad
unless success?
puts 'failure'
else
puts 'success'
end
# good
if success?
puts 'success'
else
puts 'failure'
end
Don't use parentheses around the condition of an if/unless/while/until
.
# bad
if (x > 10)
# body omitted
end
# good
if x > 10
# body omitted
end
Never use while/until condition do
for multi-line while/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
over while
for negative conditions.
# bad
do_something while !some_condition
# good
do_something until some_condition
Use Kernel#loop
with break rather than begin/end/until
or begin/end/while
for post-loop tests.
# bad
begin
puts val
val += 1
end while val < 0
# good
loop do
puts val
val += 1
break unless val < 0
end
Omit parentheses around parameters for methods that are part of an
internal DSL (e.g. Rake, Rails, RSpec), methods that have
"keyword" status in Ruby (e.g. attr_reader
, puts
) and attribute
access methods. Use parentheses around the arguments of all other
method invocations.
class Person
attr_reader :name, :age
# omitted
end
temperance = Person.new('Temperance', 30)
temperance.name
puts temperance.age
x = Math.sin(y)
array.delete(e)
bowling.score.should == 0
Omit parentheses for method calls with no arguments.
# bad
Kernel.exit!()
2.even?()
fork()
'test'.upcase()
# good
Kernel.exit!
2.even?
fork
'test'.upcase
Prefer {...}
over do...end
for single-line blocks. Avoid using
{...}
for multi-line blocks (multiline chaining is always
ugly). Always use do...end
for "control flow" and "method
definitions" (e.g. in Rakefiles and certain DSLs). Avoid do...end
when chaining.
names = ['Bozhidar', 'Steve', 'Sarah']
# bad
names.each do |name|
puts name
end
# good
names.each { |name| puts name }
# bad
names.select do |name|
name.start_with?('S')
end.map { |name| name.upcase }
# good
names.select { |name| name.start_with?('S') }.map { |name| name.upcase }
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 be false
.)
# 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 it name
implies it's meant to be used implicitly by case
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 $0-9
, $
,
etc. ). They are quite cryptic and their use in anything but
one-liner scripts is discouraged.
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
over Proc.new
.
# bad
p = Proc.new { |n| puts n }
# good
p = proc { |n| puts n }
Use _
for unused block parameters.
# bad
result = hash.map { |k, v| v + 1 }
# good
result = hash.map { |_, v| v + 1 }
Use $stdout/$stderr/$stdin
instead of
STDOUT/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 alias format
over the fairly
cryptic String#%
method.
# bad
'%d %d' % [20, 10]
# => '20 10'
# good
sprintf('%d %d', 20, 10)
# => '20 10'
format('%d %d', 20, 10)
# => '20 10'
Favor the use of Array#join
over the fairly cryptic Array#*
with
a string argument.
# bad
%w(one two three) * ', '
# => 'one, two, three'
# good
%w(one two three).join(', ')
# => 'one, two, three'
Use [*var]
or Array()
instead of explicit Array
check, when dealing with a
variable you want to treat as an Array, but you're not certain it's
an array.
# bad
paths = [paths] unless paths.is_a? Array
paths.each { |path| do_something(path) }
# good
[*paths].each { |path| do_something(path) }
# good (and a bit more readable)
Array(paths).each { |path| do_something(path) }
Use ranges 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)
Avoid the use of BEGIN
blocks.
Never use END
blocks. Use Kernel#at_exit
instead.
# bad
END { puts 'Goodbye!' }
# good
at_exit { puts 'Goodbye!' }
Avoid the use of flip-flops.
The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton
Name identifiers in English.
# bad - variable name written in Bulgarian with latin characters
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?
).
The names of potentially dangerous methods (i.e. methods that
modify self
or the arguments, exit!
(doesn't run the finalizers
like exit
does), etc.) should end with an exclamation mark if
there exists a safe version of that dangerous method.
# bad - there is not matching 'safe' method
class Person
def update!
end
end
# good
class Person
def update
end
end
# good
class Person
def update!
end
def update
end
end
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
over collect
, find
over detect
, select
over
find_all
, reduce
over inject
and size
over length
. 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 of select
is encouraged over find_all
is that it
goes together nicely with reject
and its name is pretty self-explanatory.
Use flat_map
instead of map
+ flatten
.
This does not apply for arrays with a depth greater than 2, i.e.
if users.first.songs == ['a', ['b','c']]
, then use map + flatten
rather than flat_map
.
flat_map
flattens the array by 1, whereas flatten
flattens it all the way.
# bad
all_songs = users.map(&:songs).flatten.uniq
# good
all_songs = users.flat_map(&:songs).uniq
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
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
over extend self
when you want
to turn a module's instance methods into class methods.
# bad
module Utilities
extend self
def parse_something(string)
# do stuff here
end
def other_utility_method(number, string)
# do some more stuff
end
end
# good
module Utilities
module_function
def parse_something(string)
# do stuff here
end
def other_utility_method(number, string)
# do some more stuff
end
end
When designing class hierarchies make sure that they conform to the Liskov Substitution Principle.
Try to make your classes as SOLID 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
. Use attr_reader
and attr_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
everything public
(which is the default). After all we're coding
in Ruby now, not in Python.
Indent the public
, protected
, and private
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. Use raise
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
Never return from an ensure
block. If you explicitly return from a
method inside an ensure
block, the return will take precedence over
any exception being raised, and the method will return as if no
exception had been raised at all. In effect, the exception will be
silently thrown away.
def foo
begin
fail
ensure
return 'very bad idea'
end
end
Use implicit begin blocks where possible.
# bad
def foo
begin
# main logic goes here
rescue
# failure handling goes here
end
end
# good
def foo
# main logic goes here
rescue
# failure handling goes here
end
Mitigate the proliferation of begin
blocks by using
contingency methods (a term coined by Avdi Grimm).
# bad
begin
something_that_might_fail
rescue IOError
# handle IOError
end
begin
something_else_that_might_fail
rescue IOError
# handle IOError
end
# good
def with_io_error_handling
yield
rescue IOError
# handle IOError
end
with_io_error_handling { something_that_might_fail }
with_io_error_handling { something_else_that_might_fail }
Don't suppress exceptions.
# bad
begin
# an exception occurs here
rescue SomeError
# the rescue clause does absolutely nothing
end
# bad
do_something rescue nil
Avoid using rescue
in its modifier form.
# bad - this catches 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 to
exit
, requiring you to kill -9
the process.
# bad
begin
# calls to exit and kill signals will be caught (except kill -9)
exit
rescue Exception
puts "you didn't really want to exit, right?"
# exception handling
end
# good
begin
# a blind rescue rescues from StandardError, not Exception as many
# programmers assume.
rescue => e
# exception handling
end
# also good
begin
# an exception occurs here
rescue StandardError => e
# exception handling
end
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
or last
over [0]
or [-1]
.
Use Set
instead of Array
when dealing with unique elements. Set
implements a collection of unordered values with no duplicates. This
is a hybrid of Array
's intuitive inter-operation facilities and
Hash
'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 fetch
when dealing with hash keys that should be present.
heroes = { batman: 'Bruce Wayne', superman: 'Clark Kent' }
# bad - if we make a mistake we might not spot it right away
heroes[:batman] # => "Bruce Wayne"
heroes[:supermann] # => nil
# good - fetch raises a KeyError making the problem obvious
heroes.fetch(:supermann)
Use fetch
with second argument to use a default value.
batman = { name: 'Bruce Wayne', is_evil: false }
# bad - if we just use || operator with falsy value we won't get the expected result
batman[:is_evil] || true # => true
# good - fetch work correctly with falsy values
batman.fetch(:is_evil, true) # => false
Prefer the use of the block instead of the default value in 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, use String#<<
. Concatenation mutates the string instance in-place
and is always faster than String#+
, 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\n some_method\n \nother_method\nend"
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
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 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
. Given
the nature of regexp in many scenarios a less command character than
(
might be a better choice for a delimiter.
# bad
%w[one two three]
%q{"Test's king!", John said.}
# good
%w(one tho 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.
__FILE__
and __LINE__
, so that your backtraces make sense:class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
define_method
is preferable to class_eval{ def ... }
When using class_eval
(or other eval
) 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, or define_method
instead. If you must use method_missing
:
respond_to_missing?
find_by_*
-- make your code as assertive as possible.super
at the end of your statement# 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
when alias_method
will do.
Use OptionParser
for parsing complex command line options and
ruby -s
for trivial command line options.
Code in a functional way, avoiding mutation when that makes sense.
Do not mutate arguments unless that is the purpose of the method.
Avoid more than three levels of block nesting.
Be consistent. In an ideal world, be consistent with these guidelines.
Use common sense.
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