styleguide/ruby/index.md
---
layout: inner
title: Ruby Style Guide
---
# The Ruby Style Guide
This Ruby style guide recommends best practices so that real-world Ruby
programmers can write code that can be maintained by other real-world Ruby
programmers. A style guide that reflects real-world usage gets used, and a
style guide that holds to an ideal that has been rejected by the people it is
supposed to help risks not getting used at all – no matter how good it is.
The guide is separated into several sections of related rules. We've tried to
add the rationale behind the rules (if it's omitted we've assumed that is pretty
obvious).
The guidelines didn't come out of nowhere. They are largely based on @bbatsov's
[ruby-style-guide](https://github.com/bbatsov/ruby-style-guide), modified
according to the sober judgement and good taste of our senior engineers. The
guide reflects feedback and suggestions from members of the Ruby community and
various highly regarded Ruby programming resources, such as
["Programming Ruby 1.9"](http://pragprog.com/book/ruby3/programming-ruby-1-9) and
["The Ruby Programming Language"](http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177).
The guide is still a work in progress, and we strongly invite your feedback --
guidelines to add, decisions you disagree with, illustrations of good or bad
practice.
> A foolish consistency is the hobgoblin of little minds
> -- [Ralph Waldo Emerson](http://www.bartleby.com/100/420.47.html)
This is a _guide_, not a _rulebook_. Break the rules with good taste, but not
capriciously. For every one of the guidelines, there is a sound argument against
it -- otherwise we wouldn't need to spell it out. Nobody needs a style guide to
say "don't write your documentation in pig latin". Reasonable people can
disagree whether `drink = if Time.now.hour > 19 then :beer else :soda end` is
clearer than `drink = (Time.now.hour > 19) ? :beer : :soda`[^1], but at
infochimps we've settled on the second. Having one uniform choice carries more
benefit than whatever fine distinction separates two close alternatives.
You can generate a PDF or an HTML copy of this guide using
[Transmuter](https://github.com/TechnoGate/transmuter).
[^1]: http://bit.ly/coffescript-says-no-to-ternary "Indeed, the authors of coffeescript outlawed the ternary (`t ? a : b`) operator"
### Table of Contents
* [Source Code Layout](#layout)
* [Documentation](#documentation)
* [Syntax](#syntax)
* [Naming](#naming)
* [Annotations](#annotations)
* [Classes](#classes)
* [Exceptions](#exceptions)
* [Collections](#collections)
* [Strings](#strings)
* [Regular Expressions](#regexps)
* [Percent Literals](#percent_literals)
* [Metaprogramming](#metaprogramming)
* [Setup](#setup)
* [Misc](#misc)
<a name="layout"></a>
## Source Code Layout
> 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... <br/>
> -- Jerry Coffin (on indentation)
* Use `UTF-8` as the source file encoding.
* Use two **spaces** per indentation level.
```Ruby
# good
def some_method
do_something
end
# bad - four spaces
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```
* Use spaces around operators, after commas, colons and semicolons,
and before `}`. Whitespace might be (mostly) irrelevant to the Ruby
interpreter, but its proper use is the key to writing easily
readable code.
```Ruby
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:
```Ruby
# bad
e = M * c ** 2
# good
e = M * c**2
```
* No spaces after `(`, `[`, `{`, or before `]`, `)`.
```Ruby
some(arg).other
[1, 2, 3].length
[1, 2, 3].each{|e| puts e }
```
* Indent `when` as deep as `case`.
```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
# 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
# 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
```
* Use empty lines between `def`s and to break up a method into logical
paragraphs.
- However, multiple long paragraphs in a method is a smell -- consider
moving each into a small self-documenting method.
```Ruby
def some_method
data = initialize(options)
data.manipulate!
data.result
end
def some_method
result
end
```
* If the parameters of a method call span multiple lines, move all of them down to read in parallel.
```Ruby
# 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 (hanging way out in space):
def send_mail(source)
Mailer.deliver(to => 'bob@example.com',
from => 'us@example.com',
subject => 'Important message',
body => source.text)
end
# bad (inconsistent indentation):
def send_mail(source)
Mailer.deliver(to => 'bob@example.com',
from => 'us@example.com',
subject => 'Important message',
body => source.text)
end
# good (can easily read down the list of keys and list of values)
def send_mail(source)
Mailer.deliver(
to => 'bob@example.com',
from => 'us@example.com',
subject => 'Important message',
body => source.text)
end
```
* Align parallel constructions or assignments: it makes the code easier to read,
and highlights parallel functionality.
```Ruby
# bad
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
helicity = hemiconducer.cromulence ** 2
reluctance = hemiconducer.reluctor.reluctance
phase = moon.phase - average_marzelvane_phase
```
* Don't be over-DRY -- a repeated clause, written in parallel, is easier to read
than a trivial loop:
```Ruby
# bad
[ :flux, :phrasal, :nimbus ].each do |capacitor_type|
counterrotate_capacitor capacitor_type, moon.phase, reluctance
end
# good
counterrotate_capacitor :flux, moon.phase, reluctance
counterrotate_capacitor :phrasal, moon.phase, reluctance
counterrotate_capacitor :nimbus, moon.phase, reluctance
```
let good taste be your guide, but when lines of code are equivalent prefer the
small multiple over the explicit loop.
* Indent `protected`, `public`, `private` and `module_function` at the same
level as the enclosing declaration.
- good:
```Ruby
module Validations
def valid?(context = nil)
current_context, self.validation_context = validation_context, context
errors.clear
run_validations!
ensure
self.validation_context = current_context
end
# ...
protected
def run_validations!
run_callbacks :validate
errors.empty?
end
end
```
- bad (easy to read past):
```Ruby
module Validations
def valid?
# ....
end
protected
def run_validations!
# ...
end
end
```
- bad (inconsistent indentation, editors will screw up):
```Ruby
module Validations
def valid?
# ....
end
protected
def run_validations!
# ...
end
end
```
* Keep lines fewer than 120 characters.
* Remove trailing whitespace.
* Convert all tabs to spaces.
<a name="documentation"></a>
## Documentation
> 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. <br/>
> -- Steve McConnell
* Use YARD and its conventions for API documentation.
* Don't put an empty line between the comment block and the `def`.
* Avoid superfluous comments:
```Ruby
# bad: adds nothing to my understanding
# convert the model to xml
def to_xml
# ...
end
# good: method name tells me everything I need to know.
def to_xml
# ...
end
* For text files and complex documentation blocks, use
[Markdown](http://daringfireball.net/projects/markdown/syntax) (not textile,
plain text or RDoc).
### Internal comments
* Write self-documenting code and ignore the rest of this section. Seriously!
* Internal comments are often a smell that a method should be broken up:
```Ruby
# bad: defocused
def adjust_hemiconducer_circuit(sagacity)
# align the marzelvanes
... 4 lines ...
# calculate moon phase and reluctance
... 7 lines ..
# counterrotate the plenum and flux capacitors
... 12 lines ...
end
# good: story doesn't get in the way of the plot
def adjust_hemiconducer_circuit(sagacity)
align_marzelvanes(sagacity)
moon = Moon.current
reluctance = Reluctor.find_reluctance(:sagacity => sagacity)
counterrotate_capacitor :plenum, moon.phase, reluctance
counterrotate_capacitor :nimbus, moon.phase, reluctance
end
```
* Comments longer than a word are capitalized and use punctuation. Use [one
space](http://en.wikipedia.org/wiki/Sentence_spacing) after periods.
* Here again: avoid superfluous comments.
```Ruby
# bad
counter += 1 # increments counter by one
```
* Keep existing comments up-to-date. No comment is better than an outdated
comment.
* Avoid writing comments to explain bad code. Refactor the code to
make it self-explanatory. (Do or do not - there is no try.)
<a name="syntax"></a>
## Syntax
* Use `def` with parentheses when there are arguments. Omit the
parentheses when the method doesn't accept any arguments.
```Ruby
def some_method
# body omitted
end
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.
```Ruby
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`.
```Ruby
# bad
if some_condition then
# body omitted
end
# good
if some_condition
# body omitted
end
```
* Favor the ternary operator(`?:`) over `if/then/else/end` constructs. It's
more common and obviously more concise. Group complex sub-clauses in
parentheses.
```Ruby
# bad
result = if some_condition then something else something_else end
# good
result = some_condition ? something : something_else
# bad (needs parens)
drinks = age > 18 ? ['beer', 'wine'] : ['shirley temple']
# good
drinks = (age > 18) ? ['beer', 'wine'] : ['shirley temple']
```
* 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.
```Ruby
# 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; ...` (with a semicolon). Also never use `if x: ...` (with a
colon) - it is not only bad form but it has been removed in Ruby 1.9. Use the
ternary operator instead.
```Ruby
# bad
result = if some_condition: something else something_else end
# bad
result = if some_condition; something else something_else end
# good
result = some_condition ? something : something_else
```
* Use `when x then ...` for one-line cases. The alternative syntax
`when x: ...` is removed in Ruby 1.9.
* 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.)
```Ruby
# boolean expression
if some_condition && some_other_condition
do_something
end
# control flow
document.saved? or document.save!
```
- us `and/or` implies "don't worry about this
* 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 `and/or`.
```Ruby
# bad
if some_condition
do_something
end
# good
do_something if some_condition
# another good option
some_condition and do_something
```
* Favor `unless` over `if` for negative conditions (or control
flow `or`).
```Ruby
# bad
do_something if not some_condition
# good
do_something unless some_condition
# another good option
some_condition or do_something
```
* Prefer `not` to `!` -- it's more visible. Always parenthesize a `not` clause
in a compound expression.
* Never use `unless` with `else`. Rewrite these with the positive case first.
```Ruby
# bad
unless success?
puts 'failure'
else
puts 'success'
end
# good
if success?
puts 'success'
else
puts 'failure'
end
```
* Don't use parentheses around a simple condition in an `if/unless/while`,
unless the condition contains an assignment (see "Using the return value
of `=`" below).
```Ruby
# bad
if (x > 10)
# body omitted
end
# good
if x > 10
# body omitted
end
# ok
if (x = self.next_value)
# 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.
```Ruby
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)
```
* 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.
```Ruby
names = ["Bozhidar", "Steve", "Sarah"]
# good
names.each{|name| puts name }
# bad
names.each do |name|
puts name
end
# good
names.select{|name| name.start_with?("S") }.map{|name| name.upcase }
# bad
names.select do |name|
name.start_with?("S")
end.map{|name| name.upcase }
```
Some will argue that multiline chaining would look OK with the use of {...}, but they should
ask themselves - it this code really readable and can't the blocks contents be extracted into
nifty methods.
* Avoid `return` where not required.
```Ruby
# 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:
```Ruby
# 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.
```Ruby
# 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.
```Ruby
# good - shows intented 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.
```Ruby
# set name to Bozhidar, only if it's nil or false
name ||= 'Bozhidar'
```
* Don't use `||=` to initialize boolean variables or missing hash
values. (Consider what would happen if the current value happened to be
`false`.)
```Ruby
# bad - would set enabled to true even if it was false
enabled ||= true
# good
enabled = true if enabled.nil?
# bad
nuke[:launch] ||= default_launch_state
# good
nuke[:launch] = default_launch_state unless nuke.has_key?(:launch)
```
* 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.
```Ruby
# 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)`.
* In an expression with multiple parentheses, tastefully insert whitespace to
let the reader more easily pair open/close parens and see groups.
```Ruby
# bad (a petty consistency is
# good
quad_1 = (-b + Math.sqrt( b**2 + (4 * a * c) )) / (2 * a)
quad_1 = (-b + Math.sqrt( b**2 - (4 * a * c) )) / (2 * a)
```
* Always run the Ruby interpreter with the `-w` option so it will warn
you if you forget either of the rules above!
* Use `_` for unused block parameters.
```Ruby
# bad
result = hash.map{|k, v| v + 1 }
# good
result = hash.map{|_, v| v + 1 }
```
### Ruby 1.9-only sugar
For all internal projects and most external projects we have abandoned ruby 1.8
compatibility. The exceptions are Wukong, *all* cookbooks, ironfan, configilere,
and most of gorillib. Outside of those:
* When the keys of your hash are symbols you may use the Ruby 1.9 hash
literal syntax.
```Ruby
# good
hash = { :one => 1, :two => 2 }
# if project is 1.9-only and keys are only symbols
hash = { one: 1, two: 2 }
```
* You should use the new lambda literal syntax *unless* 1.8-compatibility is
required. Omit parentheses if there are no arguments to the block.
Avoid situations where understanding the subtle differences between Procs and lambda is required, i.e. returning.
Prefer `->` over `lambda` over `Proc.new`.
```Ruby
# bad
adder = lambda{|a, b| a + b }
adder.call(1, 2)
id_generator = Proc.new{ [Time.now.to_f, $!, rand].join('-') }
# good
adder = ->(a, b){a + b }
adder.(1, 2)
id_generator = ->{ [Time.now.to_f, $!, rand].join('-') }
```
<a name="naming"></a>
## Naming
> The only real difficulties in programming are cache invalidation and
> naming things. <br/>
> -- Phil Karlton
> ... and off by one errors
> -- apocryphal
* Use `underscore_case` for methods and variables.
* Use `CamelCase` for classes and modules. Even acronyms like HTTP,
RFC, XML should be camelcased: `HttpRequest`, `XmlDoc`.
* The `CamelCase` and `underscore_case` should always agree:
```Ruby
# bad (missing underscore)
twitteruser = TwitterUser.new('bob')
# good
twitter_user = TwitterUser.new('bob')
```
* Use `ALL_CAPS` for other constants.
* Do not use `lowerCamelCase` in any context.
* The names of predicate methods (methods that return a boolean value)
should end in a question mark. (e.g. `Array#empty?`).
* Method names should end with an exclamation point when they are:
- potentially "dangerous": `launch_nukes!`, `db_table.drop!`
- have suprising side effects: modify `self` or the arguments, `exit!`
- in rare cases (notably `ActiveRecord`), an exclamation point indicates the
'loud' (exception-raising) version of a method that normally returns false
on failure. Use this sparingly -- it's not assertive, and makes it easy to
ignore necessary error handling.
* When using `Array` methods with short blocks, name a generic argument `|el|`
-- do not use `|e|` or other variants. If they are not generic, use
precise names (`|user|`).
* When using `Hash` methods with short blocks, name generic arguments `|key, val|`
-- do not use `|k, v|` or other variants. If they are not generic, use
precise names (`|user_id, user_name|`). If it is a named-record mapping, name
the arguments `something_name` and `something_info`:
```Ruby
players = { cal: { id: 8, team: 'BAL' }, pedro: { id: 45, team: 'BOS' }, }
players.each do |player_name, player_info|
# ...
end
```
* When using `reduce` with short blocks, name the arguments `|acc, el|`
(accumulator, element).
* When defining binary operators, name the argument `other`.
```Ruby
def +(other)
# body omitted
end
```
* Prefer `map` over `collect`, `find` over `detect`, `select` over
`find_all`, `inject` over `reduce`. No preference between `size` and `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.
<a name="annotations"></a>
## Annotations
* Annotations should 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 `#`.
```Ruby
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.
```Ruby
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?`
* Don't use other custom annotation keywords.
<a name="classes"></a>
## Classes
* When designing class hierarchies make sure that they conform to the
[Liskov Substitution Principle](http://en.wikipedia.org/wiki/Liskov_substitution_principle) --
roughly, subclasses should behave like their ancestors.
- In particular, don't put Abstract Factory methods on a superclass if they don't make sense on a subclass.
* 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.
```Ruby
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.
```Ruby
# 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
```
* Consider adding factory methods to provide additional sensible ways
to create instances of a particular class.
```Ruby
class Person
def self.create(options_hash)
# body omitted
end
end
```
* Prefer [duck-typing](http://en.wikipedia.org/wiki/Duck_typing) over inheritance.
```Ruby
# 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.
```Ruby
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.
- If the attribute is not visible, use class instance variables
- If the attribute is visible, use `class_attribute` (from eg. gorillib). Be
careful to not modify parent `class_attribute`s in place.
* 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).
* Indent the `public`, `protected`, and `private` methods as much the
enclosing scope they apply to. Leave one blank line above and below them.
```Ruby
class SomeClass
def public_method
# ...
end
private
def private_method
# ...
end
end
* Use `def self.method` to define class methods. This makes the methods
more resistant to refactoring changes.
```Ruby
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
```
<a name="exceptions"></a>
## Exceptions
* Don't suppress exceptions.
```Ruby
begin
# an exception occurs here
rescue SomeError
# the rescue clause does absolutely nothing
end
```
* Don't use exceptions for flow of control.
```Ruby
# bad
begin
n / d
rescue ZeroDivisionError
puts "Cannot divide by 0!"
end
# good
if d.zero?
puts "Cannot divide by 0!"
else
n / d
```
* Do not rescue the `Exception` class. `StandardError` is the most
reasonable catch-all, but you should rescue the most precise error
you can.
```Ruby
# bad
begin
# an exception occurs here
rescue
# exception handling
end
# still bad
begin
# an exception occurs here
rescue Exception
# exception handling
end
# better
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.
```Ruby
# bad
begin
# some code
rescue StandardError => e
# some handling
rescue ArgumentError => e
# some handling
end
# good
begin
# some code
rescue ArgumentError => e
# some handling
rescue StandardError => e
# some handling
end
```
* Release external resources obtained by your program in an ensure
block.
```Ruby
f = File.open("testfile")
begin
# .. process
rescue
# .. handle error
ensure
f.close unless f.nil?
end
```
* Custom exceptions should inherit from the most specific appropriate class in
the standard library. Override the `to_s` method, not the `message` method.
* In most cases however, raise an exception with specific information. Put
single quotes around values (so that blank values are visible). Avoid using
`<` and `>` in error messages.
```Ruby
raise ArgumentError, "Animals must enter ark two-by-two: got '#{animal_1}', '#{animal_2}'" unless (animal_1.species == animal_2.species)
raise ArgumentError, "Ark cannot hold imaginary animals: got '#{animal_1}', '#{animal_2}'" if animal_1.imaginary? || animal_2.imaginary?
```
<a name="collections"></a>
## Collections
* Prefer `%w` to the literal array syntax when you need an array of
tokens. Always use `%w[ ... ]`, and leave a space at the start and end.
```Ruby
# bad
STATES = ['draft', 'open', 'closed']
# bad (wrong brackets)
STATES = %w(draft open closed)
# good
STATES = %w[ draft open closed ]
```
* Avoid the creation of huge gaps in arrays.
```Ruby
arr = []
arr[100] = 1 # now you have an array with lots of nils
```
* 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.
* Use symbols instead of strings as hash keys.
```Ruby
# bad
hash = { 'one' => 1, 'two' => 2, 'three' => 3 }
# good
hash = { one: 1, two: 2, three: 3 }
```
* Avoid the use of mutable object as hash keys.
* Use the new 1.9 literal hash syntax in preference to the hashrocket
syntax.
```Ruby
# bad
hash = { :one => 1, :two => 2, :three => 3 }
# good
hash = { one: 1, two: 2, three: 3 }
```
* Rely on the fact that hashes in 1.9 are ordered.
* Never modify a collection while traversing it.
<a name="strings"></a>
## Strings
* Prefer string interpolation or array-with-join over string concatenation:
```Ruby
# bad
email_with_name = user.name + ' <' + user.email + '>'
# good (string is short)
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.
```Ruby
# bad
name = "Bozhidar"
# good
name = 'Bozhidar'
```
* Use `{}` around instance variables being interpolated into a string.
```Ruby
# bad (too clever)
def to_s
"#@first_name #@last_name"
end
# good
def to_s
"#{@first_name} #{@last_name}"
end
```
* Avoid using `String#+` when you need to construct large data chunks. Instead,
use `String#<<` or build up an array and us `#join`. Concatenation mutates the
string instance in-place and is always faster than `String#+`, which creates a
bunch of new string objects.
```Ruby
# good and also fast
html = ''
html << '<h1>Page title</h1>'
paragraphs.each do |paragraph|
html << "<p>#{paragraph}</p>"
end
# ok, because there's no conditional logic
def to_s
[ scheme, ':',
'//', authority,
path,
'?', query_string,
'#', fragment
].join
end
# good
def to_s
uri_str = ''
uri_string << "#{scheme}:" unless scheme.nil?
uri_string << "//#{authority}" unless authority.nil?
uri_string << path.to_s
uri_string << "?#{query_string}" unless query_string.nil?
uri_string << "##{fragment}" unless fragment.nil?
uri_string
end
```
<a name="regexps"></a>
## 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.
```Ruby
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.
```Ruby
/(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 (but note that the regexp must precede the string):
```Ruby
# 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`. Never use `\Z`.
```Ruby
string = "some injection\nusername"
string[/^username$/] # matches
string[/\Ausername\z/] # don't match
```
* Use `x` modifier for complex regexps. This makes them more readable and you
can add some useful comments. Just be careful as spaces are ignored.
```Ruby
regexp = %r{
start # some text
\s # white space char
(group) # first group
(?:alt1|alt2) # some alternation
end
}x
```
* For complex replacements `sub`/`gsub` can be used with block or hash.
<a name="percent_literals"></a>
## Percent Literals
* Use `%w` freely (use square brackets always, since it is an array):
```Ruby
STATES = %w[ draft open closed ]
```
* Use `%Q{}` for single-line strings which require both interpolation and
embedded double-quotes. Do not use `%{}` (no `Q`) and do not use `%Q()` (wrong
brackets). For multi-line strings, prefer heredocs.
```Ruby
# bad (no interpolation needed)
%Q{<div class="text">Some text</div>}
# should be '<div class="text">Some text</div>'
# or %q{<div class="text">Some text</div>}
# bad (no need for fanciness)
%Q{This is #{quality} style}
# should be "This is #{quality} style"
# bad (multiple lines)
%Q{<div>\n<span class="big">#{exclamation}</span>\n</div>}
# should be a heredoc.
# good (requires interpolation, has quotes, single line)
%Q{<tr><td class="name">#{name}</td>}
```
* Use `%r{}` for regular expressions matching one or more '/' characters.
```Ruby
# bad
%r(\s+)
# good
%r{^/(.*)$}
%r{^/blog/2011/(.*)$}
```
* Avoid `%x`, `%s`, `%W` and plain `%{}`.
* Prefer `{}` as delimiters for all string-like literals, and `[]` for `%w`.
<a name="metaprogramming"></a>
## Metaprogramming
Use metaprogramming sparely. Metaprogramming should only occur in frameworks,
not applications -- it is justified to abstract a widely-repeated pattern of
long use, and rarely otherwise.
* Our canonical language is *Ruby 1.9.2+ plus Gorillib's extensions*.
- Do not otherwise mess around (monkey patch) with core classes.
- Do not bring in other code from ActiveSupport, extlib or the like. Exception:
if you are writing a Rails app, chef plugin, or other fully
framework-immersed code, use that framework's features freely.
* Provide light predictable magic or no magic at all:
- separate sugar from fuctionality.
Good: The `collects` method doesn't do anything but dispatch to other methods.
```Ruby
# Given a class, creates a method to create-or-retrieve
#
# @example creating helper methods
# class Kitchen
# collects(Utensil)
# end
# my_kitchen = Kitchen.new
# my_kitchen.utensil 'Sauce Pot', :gallons => 5
# my_kitchen.utensil('Sauce Pot') #=> #<Utensil name="Sauce Pot" gallons=5>
#
def collects(klass)
field_name = klass.name.underscore
define_method(field_name) do |obj_name, *args, &block|
obj = registry(klass).find_or_create(obj_name)
obj.configure(*args, &block) if args.present? || block_given?
obj
end
end
```
- Options are often a smell. Encode the common case in the sugar method; the
preceding principle ensures the user can answer a necessarily complex use
case with necessarily explicit code. The resulting verbosity is a *good*
thing: the reader is left in no doubt that something unusual is being done.
- Be assertive always -- but especially when providing sugar. Light type
conversion and multiple behaviors in service of readability is great, but
don't provide multiple ways of doing the same thing.
Bad: this disastrously flexible interface can't conceivably be documented,
let alone tested.
```Ruby
#
# Get or update path to the input file.
#
# @param [Array,Pathname,String] filename - path to input file. You can pass
# in pretty much anything and it will be converted.
#
def input_file(filename=nil)
return @input_file if filename.blank?
@input_file =
case filename
when Array then File.join(filename)
when Pathname then filename
when %r{file://} then Addressable.parse(filename).path
when then File.expand_path(filename)
else raise "Don't know how to interpret filename '#{filename}'"
end
end
```
Good: makes bold, predictable choices. Want to use `file://` references?
Well tough titty toenails, do it yourself.
```Ruby
#
# Get or update path to the input file.
#
# @example
# input_file '~/skrilla.csv'
# input_file #=> '/Users/flip/skrilla.csv'
#
# @param [#to_s] filename - path to input file. You may use shell shorthand
# like '~/script.tsv' and './accounts.csv' -- they will be `expand_path`ed
# into absolute paths.
#
# @return path to input_file, nil if unset.
#
def input_file(filename=nil)
if filename then @input_file = File.expand_path(filename.to_s) ; end
@input_file
end
```
* The block form of `class_eval` is preferable to the string-interpolated
form. `define_method` is preferable to `class_eval{ def ... }`
* When using `class_eval` (or other `eval`) with string interpolation:
- Supply `__FILE__` and `__LINE__` so that your backtraces make sense:
```Ruby
class_eval "def use_relative_model_naming?; true; end", __FILE__, __LINE__
```
- add a comment block showing its appearance if interpolated:
```Ruby
# 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. Backtraces become messy; the behavior is not listed in `#methods`; misspelled method calls might silently work (`nukes.luanch_state = false`). Consider using delegation, proxy, or `define_method` instead. If you must use `method_missing`,
- be sure to define [`respond_to_missing?`](http://robots.thoughtbot.com/post/28335346416/always-define-respond-to-missing-when-overriding) (1.9 only; it means you don't have to [also define `respond_to?`](http://devblog.avdi.org/2011/12/07/defining-method_missing-and-respond_to-at-the-same-time/))
- call `super` at the end of your statement
- only catch methods with a well-defined prefix, such as `find_by_*` -- make your code as assertive as possible.
- delegate to assertive, non-magical methods, named for that prefix:
```Ruby
# bad
def method_missing?(meth, *args, &block)
if /^find_by_(?<prop>.*)/ =~ meth.to_s
# ... 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
```
* avoid Aliasing/Redefining methods. Instead, generate a `Module` and inject it.
- calling `super` is a good idea.
- if you're going to monkey patch, make sure that the method isn’t already there.
<a name="setup"></a>
## Setup
* Include a `README.md` that includes all installation steps.
* Use [Markdown](http://daringfireball.net/projects/markdown/syntax), not textile, plain text or RDoc.
* Include a `Procfile` if there are processes to start.
* Include a `Gemfile`. If the project is a standalone app, you should check
`Gemfile.lock` in to the repo. If it is not deployed independently, you should
exclude `Gemfile.lock`.
* Do not version an `.rvmrc` file into a repo.
<a name="misc"></a>
## Misc
* Write `ruby -w` safe code.
* Avoid hashes as optional parameters. Does the method do too much?
* 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.
```Ruby
#bad
$foo_bar = 1
#good
class Foo
class_attribute :bar
end
Foo.bar = 1
```
* Avoid `alias` when `alias_method` will do.
* Use `Configliere` for parsing command line options.
* Code in a functional way, avoiding mutation when that makes sense.
* Avoid needless metaprogramming.
* 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.