A mostly reasonable approach to Ruby
(forked from bbatsov's style guide)
- Source Code Layout
- Syntax
- Naming
- Comments
- Classes
- Exceptions
- Collections
- Strings
- Regular Expressions
- Percent Literals
- Metaprogramming
- Misc
- Tools
- Contributing
-
Use
UTF-8
as the source file encoding. -
Use two space indentation (aka soft tabs). No hard tabs.
-
Use Unix-style line endings.
-
No trailing whitespace.
-
Don't use semicolons. Use one expression per line.
# bad puts 'foobar'; puts 'foo'; puts 'bar' # good puts 'foobar' puts 'foo' puts 'bar' puts 'foo', 'bar' # this applies to puts in particular
-
Use a single-line format for class definitions with no body.
# bad class FooError < StandardError end # good class FooError < StandardError; end
-
Don't use single-line methods.
# bad def some_method() body end # good def some_method body end def no_op; end #empty-body methods are okay
-
Use spaces around operators, after commas, colons and semicolons, around
{
and before}
.sum = 1 + 2 a, b = 1, 2 1 > 2 ? true : false def no_op; end [1, 2, 3].each { |e| puts e } # Only exception is the exponent operator: # bad e = M * c ** 2 # good e = M * c**2
-
Pad Hash literals with a single space.
# bad {one: 1, two: 2} # good { one: 1, two: 2 }
-
No spaces for embedded expression.
# bad "string#{ expr }" # good "string#{expr}"
-
No space padding inside parens
()
or brackets[]
.#bad some( arg ).other [ 1, 2, 3 ].size #good some(arg).other [1, 2, 3].size
-
No space after
!
.# bad ! something # good !something
-
Indent
when
as deep ascase
. 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
-
Indent conditional expression variable assignments by one soft tab, beneath the variable assignment.
# bad 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 # bad 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 # good 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 # bad result = if some_cond calc_something else calc_something_else end # bad result = if some_cond calc_something else calc_something_else end # good result = if some_cond calc_something else calc_something_else end
-
Use empty lines between method definitions and also to break up a method into logical paragraphs internally.
def some_method data = initialize(options) data.manipulate! data.result end def some_method result end
-
Don't use comma after the last parameter in a method call.
# bad - easier to move/add/remove parameters, but still not preferred some_method( size, count, color, ) # good 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
-
Don't use line continuation
\
for anything but string concatenation.# bad result = 1 - \ 2 # good long_string = 'First part of the long string' \ ' and second part of the long string'
-
Use the dot
.
on new lines when method chaining.# 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
-
Use multiple lines if the parameters of a method call result in a long line. Align the parameters with a single indent.
# bad def send_mail(source) Mailer.deliver(to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text) end # good def send_mail(source) Mailer.deliver( to: '[email protected]', from: '[email protected]', subject: 'Important message', body: source.text ) end
-
Align the elements of array literals spanning multiple lines.
# bad - single indent menu_item = ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam'] # 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' ]
-
Use underscores on large numeric literals to improve their readability.
# bad num = 1000000 # good 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
. -
Don't use block comments.
# bad == begin comment line another comment line == end # good # comment line # another comment line
-
Use
::
only to reference constants(this includes classes and modules) and constructors (likeArray()
orNokogiri::HTML()
). Never use::
for regular method invocation.# bad SomeClass::some_method some_object::some_method # good SomeClass.some_method some_object.some_method SomeModule::SomeClass::SOME_CONST SomeModule::SomeClass()
-
Use
def
with parentheses when there are arguments. Omit the parentheses when the method doesn't accept any arguments.# bad def some_method() # body omitted end # good def some_method # body omitted end # bad def some_method arg1, arg2 # body omitted end # good def some_method(arg1, arg2) # body omitted end
-
Never use
for
, unless you know exactly why. Most of the time iterators should be used instead.for
is implemented in terms ofeach
(so you're adding a level of indirection), but with a twist -for
doesn't introduce a new scope (unlikeeach
) and variables defined in its block will be visible outside it.arr = [1, 2, 3] # bad for elem in arr do puts elem end # note that elem is accessible outside of the for loop elem #=> 3 # good arr.each { |elem| puts elem } # elem is not accessible outside each's block elem #=> NameError: undefined local variable or method `elem'
-
Never use
then
for multi-lineif/unless
.# bad if some_condition then # body omitted end # good if some_condition # body omitted end
-
Use the ternary operator(
?:
) overif/then/else/end
constructs. It's more common and obviously more concise.# bad result = if some_condition then something else something_else end # good result = some_condition ? something : something_else
-
Use one expression per branch in a ternary operator. This also means that ternary operators must not be nested. Prefer
if/else
constructs in these cases.# bad some_condition ? (nested_condition ? nested_something : nested_something_else) : something_else # good if some_condition nested_condition ? nested_something : nested_something_else else something_else end
-
Never use
if x: ...
- as of Ruby 1.9 it has been removed. Use the ternary operator instead.# bad result = if some_condition: something else something_else end # good result = some_condition ? something : something_else
-
Never use
if x; ...
. Use the ternary operator instead. -
Use
when x then ...
for one-line cases. The alternative syntaxwhen x: ...
has been removed as of Ruby 1.9. -
Never use
when x; ...
. See the previous rule. -
Use
!
instead ofnot
.# bad - braces are required because of op precedence x = (not something) # good x = !something
-
Avoid the use of
!!
.# bad x = 'test' # obscure nil check if !!x # body omitted end x = false # double negation is useless on booleans !!x # => false # good x = 'test' unless x.nil? # body omitted end
-
Never use
and
oror
. Use&&
and||
instead. -
Avoid multi-line
?:
ternary operators. Useif/unless
instead. -
Use the
if/unless
modifier when you have a single-line body.# bad if some_condition do_something end # bad - obscure control flow some_condition && do_something # good do_something if some_condition
-
Use
unless
overif
for negative conditions.# bad do_something if !some_condition # bad do_something if not some_condition # bad - obscure control flow some_condition || do_something # good do_something unless some_condition
-
Never use
unless
withelse
. Rewrite these with the positive case first.# bad unless success? puts 'failure' else puts 'success' end # good if success? puts 'success' else puts 'failure' end
-
Don't use parentheses around the condition of an
if/unless/while/until
.# bad if (x > 10) # body omitted end # good if x > 10 # body omitted end
-
Never use
while/until condition do
for multi-linewhile/until
.# bad while x > 5 do # body omitted end until x > 5 do # body omitted end # good while x > 5 # body omitted end until x > 5 # body omitted end
-
Favor modifier
while/until
usage when you have a single-line body.# bad while some_condition do_something end # good do_something while some_condition
-
Favor
until
overwhile
for negative conditions.# bad do_something while !some_condition # good do_something until some_condition
-
Use
begin/end/until
orbegin/end/while
rather thanKernel#loop
with break for post-loop tests.# bad loop do puts val val += 1 break unless val < 0 end # good begin puts val val += 1 end while val < 0
-
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. Always use parenthesis if the result of the method is used or stored.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
-
Use
{...}
overdo...end
for single-line blocks. -
Use
do...end
over{...}
for multi-line blocks. -
Always use
do...end
for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs). -
Don't use
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 } # good names .select { |name| name.start_with?('S') } .map { |name| name.upcase }
-
Consider using explicit block argument to avoid writing block literal that just passes its arguments to another block. 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 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. (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
-
Avoid using 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 assignments in conditional expressions if it helps reduce nested conditionals.
# bad - nested conditionals if conditional else v = method(foo) if v do_something(v) end end # bad - repeated method call if conditional elsif method(foo) do_something(method(foo) end # good if conditional elsif (v = method(foo)) do_something(v) end
-
Use
||=
freely to initialize variables.# set name to Bozhidar, only if it's nil or false name ||= 'Bozhidar'
-
Don't use
||=
to initialize boolean variables. (Consider what would happen if the current value happened to befalse
.)# bad - would set enabled to true even if it was false enabled ||= true # good enabled = true if enabled.nil?
-
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 if something something = something.downcase end # ok something = something.downcase if something # good something = something && something.downcase # better 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. 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.call()
overproc.()
orproc[]
for both lambdas and procs.# bad - looks similar to Enumeration access l = ->(v) { puts v } l[1] # bad l = ->(v) { puts v } l.(1) # good l = ->(v) { puts v } l.call(1)
-
Use
_
for unused block parameters.# bad result = hash.map { |k, v| v + 1 } # good result = hash.map { |_, v| v + 1 }
-
Use
$stdout/$stderr/$stdin
instead ofSTDOUT/STDERR/STDIN
.STDOUT/STDERR/STDIN
are constants, and while you can actually reassign (possibly to redirect some stream) constants in Ruby, you'll get an interpreter warning if you do so. -
Use
warn
instead of$stderr.puts
. Apart from being more concise and clear,warn
allows you to suppress warnings if you need to (by setting the warn level to 0 via-W0
). -
Favor the use of
sprintf
and its aliasformat
over the fairly crypticString#%
method.# bad '%d %d' % [20, 10] # => '20 10' # good sprintf('%d %d', 20, 10) # => '20 10' # good sprintf('%{first} %{second}', first: 20, second: 10) # => '20 10' format('%d %d', 20, 10) # => '20 10' # good format('%{first} %{second}', first: 20, second: 10) # => '20 10'
-
Use
Array#join
overArray#*
.# bad %w(one two three) * ', ' # => 'one, two, three' # good %w(one two three).join(', ') # => 'one, two, three'
-
Use
Array()
instead of[*var]
or.is_a? Array
when dealing with a variable you want to treat as an Array.# bad [*paths].each { |path| do_something(path) } # bad paths = [paths] unless paths.is_a? Array paths.each { |path| do_something(path) } # good (and a bit more readable) Array(paths).each { |path| do_something(path) }
-
Use ranges or
Comparable#between?
instead of complex comparison logic when possible.# bad do_something if x >= 1000 && x <= 2000 # good do_something if (1000..2000).include?(x) # good do_something if x.between?(1000, 2000)
-
Favor the use of predicate methods to explicit comparisons with
==
. Numeric comparisons are OK.# bad if x % 2 == 0 end if x % 2 == 1 end if x == nil end # good if x.even? end if x.odd? end if x.nil? end if x.zero? end if x == 0 end
-
Don't use
BEGIN
blocks. -
Never use
END
blocks. UseKernel#at_exit
instead.# bad END { puts 'Goodbye!' } # good at_exit { puts 'Goodbye!' }
-
Avoid the use of flip-flops.
-
Avoid use of nested conditionals for flow of control. Prefer a guard clause when you can assert invalid data. A guard clause is a conditional statement at the top of a function that bails out as soon as it can.
# bad def compute_thing(thing) if thing[:foo] update_with_bar(thing) if thing[:foo][:bar] partial_compute(thing) else re_compute(thing) end end end # good def compute_thing(thing) return unless thing[:foo] update_with_bar(thing[:foo]) return re_compute(thing) unless thing[:foo][:bar] partial_compute(thing) end
The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton
-
Name identifiers in English.
# bad - identifier using non-ascii characters заплата = 1_000 # bad - identifier is a Bulgarian word, written with Latin letters (instead of Cyrillic) zaplata = 1_000 # good salary = 1_000
-
Use
snake_case
for symbols, methods and variables.# bad :'some symbol' :SomeSymbol :someSymbol someVar = 5 def someMethod ... end def SomeMethod ... end # good :some_symbol def some_method ... end
-
Use
CamelCase
for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.)# bad class Someclass ... end class Some_Class ... end class SomeXml ... end # good class SomeClass ... end class SomeXML ... end
-
Use
snake_case
for naming files, e.g.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.# bad - update() is potentially dangerous (in this example) class Person def update end end # good class Person def update! end end # good - update() has a safe alternative 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
(<<
and[]
are exceptions to the rule, since their semantics are different).def +(other) # body omitted end
-
Prefer
map
overcollect
,detect
overfind
,select
overfind_all
,inject
overreduce
, andlength
oversize
.-
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 overfind_all
is that it goes together nicely withreject
and its name is pretty self-explanatory.
-
-
Use
flat_map
instead ofmap
+flatten
. This does not apply for arrays with a depth greater than 2, i.e. ifusers.first.songs == ['a', ['b','c']]
, then usemap + flatten
rather thanflat_map
.flat_map
flattens the array by 1, whereasflatten
flattens it all the way.# bad all_songs = users.map(&:songs).flatten.uniq # good all_songs = users.flat_map(&:songs).uniq
-
Use
reverse_each
instead ofreverse.each
.reverse_each
doesn't do a new array allocation and that's a good thing.# bad array.reverse.each { ... } # good array.reverse_each { ... }
-
Use one space between the leading
#
character of the comment and the text of the comment. -
Avoid superfluous comments.
# bad counter += 1 # Increments counter by one.
-
Use a consistent structure in your class definitions.
class Person # extend and include go first extend SomeModule include AnotherModule # constants are next SOME_CONSTANT = 20 # afterwards we have attribute macros attr_reader :name # followed by other macros (if any) validates :name # public class methods are next in line def self.some_method end # followed by public instance methods def some_method end # protected and private methods are grouped near the end protected def some_protected_method end private def some_private_method end end
-
Prefer modules to classes with only class methods. Classes should be used only when it makes sense to create instances out of them.
# bad class SomeClass def self.some_method # body omitted end def self.some_other_method end end # good module SomeClass module_function def some_method # body omitted end def some_other_method end end
-
Favor the use of
module_function
overextend self
when you want to turn a module's instance methods into class methods.# bad module Utilities extend self def parse_something(string) # do stuff here end def other_utility_method(number, string) # do some more stuff end end # good module Utilities module_function def parse_something(string) # do stuff here end def other_utility_method(number, string) # do some more stuff end end
-
When designing class hierarchies make sure that they conform to the Liskov Substitution Principle.
-
Try to make your classes as [SOLID](http://en.wikipedia.org/wiki/SOLID_(object-oriented_design\)) as possible.
-
Always supply a proper
to_s
method for classes that represent domain objects.class Person attr_reader :first_name, :last_name def initialize(first_name, last_name) @first_name = first_name @last_name = last_name end def to_s "#{@first_name} #{@last_name}" end end
-
Use the
attr
family of functions to define trivial accessors or mutators.# bad class Person def initialize(first_name, last_name) @first_name = first_name @last_name = last_name end def first_name @first_name end def last_name @last_name end end # good class Person attr_reader :first_name, :last_name def initialize(first_name, last_name) @first_name = first_name @last_name = last_name end end
-
Avoid the use of
attr
. Useattr_reader
andattr_accessor
instead.# bad - creates a single attribute accessor (deprecated in 1.9) attr :something, true attr :one, :two, :three # behaves as attr_reader # good attr_accessor :something attr_reader :one, :two, :three
-
Consider using
Struct.new
, which defines the trivial accessors, constructor and comparison operators for you.# good class Person attr_accessor :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
-
Don't use class (
@@
) variables due to their "nasty" behavior in inheritance.class Parent @@class_var = 'parent' def self.print_class_var puts @@class_var end end class Child < Parent @@class_var = 'child' end Parent.print_class_var # => will print "child"
As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.
-
Assign proper visibility levels to methods (
private
,protected
) in accordance with their intended usage. Don't go off leaving everythingpublic
(which is the default). After all we're coding in Ruby now, not in Python. -
Indent the
public
,protected
, andprivate
methods as much the method definitions they apply to. Leave one blank line above the visibility modifier and one blank line below in order to emphasize that it applies to all methods below it.class SomeClass def public_method # ... end private def private_method # ... end def another_private_method # ... end end
-
Use
def self.method
to define singleton methods. This makes the code easier to refactor since the class name is not repeated.class TestClass # bad def TestClass.some_method # body omitted end # good def self.some_other_method # body omitted end # Also possible and convenient when you # have to define many singleton methods. class << self def first_method # body omitted end def second_method_etc # body omitted end end end
-
Don't specify
RuntimeError
explicitly in the two argument version offail/raise
.# bad fail RuntimeError, 'message' # good - signals a RuntimeError by default fail 'message'
-
Prefer supplying an exception class and a message as two separate arguments to
fail/raise
, instead of an exception instance.# bad fail SomeException.new('message') # Note that there is no way to do `fail SomeException.new('message'), backtrace`. # good fail SomeException, 'message' # Consistent with `fail SomeException, 'message', backtrace`.
-
Never return from an
ensure
block. If you explicitly return from a method inside anensure
block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised at all. In effect, the exception will be silently thrown away.def foo begin fail ensure return 'very bad idea' end end
-
Use implicit begin blocks where possible.
# bad def foo begin # main logic goes here rescue # failure handling goes here end end # good def foo # main logic goes here rescue # failure handling goes here end
-
Mitigate the proliferation of
begin
blocks by using contingency methods (a term coined by Avdi Grimm).# bad begin something_that_might_fail rescue IOError # handle IOError end begin something_else_that_might_fail rescue IOError # handle IOError end # good def with_io_error_handling yield rescue IOError # handle IOError end with_io_error_handling { something_that_might_fail } with_io_error_handling { something_else_that_might_fail }
-
Don't suppress exceptions.
# bad begin # an exception occurs here rescue SomeError # the rescue clause does absolutely nothing end # bad do_something rescue nil
-
Avoid using
rescue
in its modifier form.# bad - this catches exceptions of StandardError class and its descendant classes read_file rescue handle_error($!) # good - this catches only the exceptions of Errno::ENOENT class and its descendant classes def foo read_file rescue Errno::ENOENT => ex handle_error(ex) end
-
Don't use exceptions for flow of control.
# bad begin n / d rescue ZeroDivisionError puts 'Cannot divide by 0!' end # good if d.zero? puts 'Cannot divide by 0!' else n / d end
-
Avoid rescuing the
Exception
class. This will trap signals and calls toexit
, requiring you tokill -9
the process.# bad begin # calls to exit and kill signals will be caught (except kill -9) exit rescue Exception puts "you didn't really want to exit, right?" # exception handling end # good begin # a blind rescue rescues from StandardError, not Exception as many # programmers assume. rescue => e # exception handling end # also good begin # an exception occurs here rescue StandardError => e # exception handling end
-
Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from.
# bad begin # some code rescue Exception => e # some handling rescue StandardError => e # some handling end # good begin # some code rescue StandardError => e # some handling rescue Exception => e # some handling end
-
Release external resources obtained by your program in an ensure block.
f = File.open('testfile') begin # .. process rescue # .. handle error ensure f.close unless f.nil? end
-
Favor the use of exceptions for the standard library over introducing new exception classes.
-
Use 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 = {}
-
Use the literal array syntax vs.
%w
when you need an array of words.# bad STATES = %w(draft open closed) # good STATES = ['draft', 'open', 'closed']
-
Use the literal array syntax to
%i
when you need an array of symbols.# bad STATES = %i(draft open closed) # good STATES = [:draft, :open, :closed]
-
Avoid comma after the last item of a single-line
Array
orHash
literal.# bad VALUES = [1001, 2020, 3333, ] # good VALUES = [1001, 2020, 3333] # good - easier to move/add/remove items VALUES = [ 1001, 2020, 3333, ]
-
Avoid the creation of huge gaps in arrays.
arr = [] arr[100] = 1 # now you have an array with lots of nils
-
Use
first
orlast
over[0]
or[-1]
when accessing the first or last element from an array. -
Use
Set
instead ofArray
when dealing with unique elements.Set
implements a collection of unordered values with no duplicates. This is a hybrid ofArray
's intuitive inter-operation facilities andHash
's fast lookup. -
Prefer symbols instead of strings as hash keys.
# bad hash = { 'one' => 1, 'two' => 2, 'three' => 3 } # good hash = { one: 1, two: 2, three: 3 }
-
Avoid the use of mutable objects as hash keys.
-
Use the hash literal syntax when your hash keys are symbols.
# bad hash = { :one => 1, :two => 2, :three => 3 } # good hash = { one: 1, two: 2, three: 3 }
-
Use
Hash#key?
instead ofHash#has_key?
andHash#value?
instead ofHash#has_value?
. As noted here by Matz, the longer forms are considered deprecated.# bad hash.has_key?(:test) hash.has_value?(value) # good hash.key?(:test) hash.value?(value)
-
Use
Hash#fetch
when dealing with hash keys that should be present.heroes = { batman: 'Bruce Wayne', superman: 'Clark Kent' } # bad - if we make a mistake we might not spot it right away heroes[:batman] # => "Bruce Wayne" heroes[:supermann] # => nil # good - fetch raises a KeyError making the problem obvious heroes.fetch(:supermann)
-
Use
Hash#fetch
for default values as opposed to using custom logic.batman = { name: 'Bruce Wayne', is_evil: false } # bad - if we just use || operator with falsy value we won't get the expected result batman[:is_evil] || true # => true # good - fetch work correctly with falsy values batman.fetch(:is_evil, true) # => false
-
Prefer the use of the block instead of the default value in
Hash#fetch
.batman = { name: 'Bruce Wayne' } # bad - if we use the default value, we eager evaluate it # so it can slow the program down if done multiple times batman.fetch(:powers, get_batman_powers) # get_batman_powers is an expensive call # good - blocks are lazy evaluated, so only triggered in case of KeyError exception batman.fetch(:powers) { get_batman_powers }
-
Rely on the fact that as of Ruby 1.9 hashes are ordered.
-
Never modify a collection while traversing it.
-
Prefer string interpolation instead of string concatenation:
# bad email_with_name = user.name + ' <' + user.email + '>' # good email_with_name = "#{user.name} <#{user.email}>"
-
Prefer double-quoted strings.
# 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"
-
Use
{}
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}"
-
Use
String#<<
overString#+
for string concatenation. Concatenation mutates the string instance in-place and is always faster thanString#+
, which creates a bunch of new string objects.# bad paragraphs.each do |paragraph| html + "<p>#{paragraph}</p>" end # good paragraphs.each do |paragraph| html << "<p>#{paragraph}</p>" end
-
When using heredocs for multi-line strings keep in mind the fact that they preserve leading whitespace. It's a good practice to employ some margin based on which to trim the excessive whitespace.
code = <<-END.gsub(/^\s+\|/, '') |def test | some_method | other_method |end END #=> "def test\n some_method\n other_method\nend\n"
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.
-- Jamie Zawinski
-
Don't use regular expressions if you just need plain text search in string:
string['text']
-
For simple constructions you can use regexp directly through string index.
match = string.match(/regexp/) # get content of matched regexp first_group = string.match(/text(grp)/, 1) # get content of captured group string.match(/text (grp)/, 1) = 'replace' # string => 'text replace'
-
Use non-capturing groups when you don't use captured result of parentheses.
/(first|second)/ # bad /(?:first|second)/ # good
-
Don't use the cryptic Perl-legacy variables denoting last regexp group matches (
$1
,$2
, etc). UseRegexp.last_match[n]
instead./(regexp)/ =~ string ... # bad process $1 # good process Regexp.last_match[1]
-
Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead.
# bad /(regexp)/ =~ string ... process Regexp.last_match[1] # good /(?<meaningful_var>regexp)/ =~ string ... process meaningful_var
-
Character classes have only a few special characters you should care about:
^
,-
,\
,]
, so don't escape.
or brackets in[]
. -
Be careful with
^
and$
as they match start/end of line, not string endings. If you want to match the whole string use:\A
and\z
(not to be confused with\Z
which is the equivalent of/\n?\z/
).string = "some injection\nusername" string[/^username$/] # matches string[/\Ausername\z/] # don't match
-
Use
x
modifier for complex regexps. This makes them more readable and you can add some useful comments. Just be careful as spaces are ignored.regexp = %r{ start # some text \s # white space char (group) # first group (?:alt1|alt2) # some alternation end }x
-
For complex replacements
sub
/gsub
can be used with block or hash.
-
Use
%()
(it's a shorthand for%Q
) for single-line strings which require both interpolation and embedded double-quotes. For multi-line strings, prefer heredocs.# bad (no interpolation needed) %(<div class="text">Some text</div>) # should be '<div class="text">Some text</div>' # bad (no double-quotes) %(This is #{quality} style) # should be "This is #{quality} style" # bad (multiple lines) %(<div>\n<span class="big">#{exclamation}</span>\n</div>) # should be a heredoc. # good (requires interpolation, has quotes, single line) %(<tr><td class="name">#{name}</td>)
-
Avoid
%q
unless you have a string with both'
and"
in it. Regular string literals are more readable and should be preferred unless a lot of characters would have to be escaped in them.# bad name = %q(Bruce Wayne) time = %q(8 o'clock) question = %q("What did you say?") # good name = 'Bruce Wayne' time = "8 o'clock" question = '"What did you say?"'
-
Use
%r
only for regular expressions matching more than one '/' character.# bad %r(\s+) # still bad %r(^/(.*)$) # should be /^\/(.*)$/ # good %r(^/blog/2011/(.*)$)
-
Avoid the use of
%x
unless you're going to invoke a command with backquotes in it(which is rather unlikely).# bad date = %x(date) # good date = `date` echo = %x(echo `date`)
-
Avoid the use of
%s
. It seems that the community has decided:"some string"
is the preferred way to created a symbol with spaces in it. -
Prefer
()
as delimiters for all%
literals, except%r
. Since braces often appear inside regular expressions in many scenarios a less common character like{
might be a better choice for a delimiter, depending on the regexp's content.# bad %w[one two three] %q{"Test's king!", John said.} # good %w(one two three) %q("Test's king!", John said.)
-
Avoid needless metaprogramming.
-
Do not mess around in core classes when writing libraries. (Do not monkey-patch them.)
-
The block form of
class_eval
is preferable to the string-interpolated form.-
when you use the string-interpolated form, always supply
__FILE__
and__LINE__
, so that your backtraces make sense:class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
-
define_method
is preferable toclass_eval{ def ... }
-
-
When using
class_eval
(or othereval
) with string interpolation, add a comment block showing its appearance if interpolated (a practice used in Rails code):# from activesupport/lib/active_support/core_ext/string/output_safety.rb UNSAFE_STRING_METHODS.each do |unsafe_method| if 'String'.respond_to?(unsafe_method) class_eval <<-EOT, __FILE__, __LINE__ + 1 def #{unsafe_method}(*args, &block) # def capitalize(*args, &block) to_str.#{unsafe_method}(*args, &block) # to_str.capitalize(*args, &block) end # end def #{unsafe_method}!(*args) # def capitalize!(*args) @dirty = true # @dirty = true super # super end # end EOT end end
-
Avoid using
method_missing
for metaprogramming because backtraces become messy, the behavior is not listed in#methods
, and misspelled method calls might silently work, e.g.nukes.launch_state = false
. Consider using delegation, proxy, ordefine_method
instead. If you must usemethod_missing
:-
Be sure to also define
respond_to_missing?
-
Only catch methods with a well-defined prefix, such as
find_by_*
-- make your code as assertive as possible. -
Call
super
at the end of your statement -
Delegate to assertive, non-magical methods:
# bad def method_missing?(meth, *args, &block) if /^find_by_(?<prop>.*)/ =~ meth # ... lots of code to do a find_by else super end end # good def method_missing?(meth, *args, &block) if /^find_by_(?<prop>.*)/ =~ meth find_by(prop, *args, &block) else super end end # best of all, though, would to define_method as each findable attribute is declared
-
-
Write
ruby -w
safe code. -
Avoid hashes as optional parameters. Does the method do too much? (Object initializers are exceptions for this rule).
-
Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC.
-
Avoid parameter lists longer than three or four parameters.
-
If you really need "global" methods, add them to Kernel and make them private.
-
Use module instance variables instead of global variables.
# bad $foo_bar = 1 #good module Foo class << self attr_accessor :bar end end Foo.bar = 1
-
Avoid
alias
whenalias_method
will do. -
Use
OptionParser
for parsing complex command line options andruby -s
for trivial command line options. -
Prefer
Time.now
overTime.new
when retrieving the current system time. -
Code in a functional way, avoiding mutation when that makes sense.
-
Do not mutate arguments unless that is the purpose of the method.
-
Avoid more than three levels of block nesting.
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.
This work is licensed under a Creative Commons Attribution 3.0 Unported License