Ruby Style Guide

Please note: This is a work in progress

I'm making changes to the guidelines according to my personal preferences, and adding code examples to support each point.

I'd also like to include JavaScript and other programming languages eventually. See Felix's Node.js Style Guide for a Node.js style guide template.

Goals

This style guide is an attempt to help me identify and understand the subset of the Ruby programming language I commonly employ. I believe this set of rules and guidelines yields the most satisfying style to write, and more importantly, read code in Ruby.

The primary activity of a programmer is not to write code. It is to read code. This is often code written by the same programmer. Code is most easily read when its formatting provides cues about its internal structure, and its semantics reveal knowledge and insight about its domain and purpose. The key elements of coding style are thus formatting and naming.

Code is useless unless it performs tasks reliably within a reasonable amount of time. Performance considerations are therefore important factors in developing and adapting coding style over time.

Disclaimer

I do not write the most beautiful code in the Universe, and following these guidelines will not necessarily lead to writing beautiful code.

Formatting

Never use more than 80 characters per line

This is the single most important rule. If you only follow one rule, please let it be this rule. Many other rules are derived or altered by this rule.

As an example, suppose you have a long list of options to pass into an ActiveRecord object

Person.create(:first_name => 'Adam', :last_name => 'Smith', :occupation => 'Philosopher', :date_of_birth => '1723-06-23', :karma => 17900717, :email => 'adam.smith@example.com')

Without looking at the example again, how many options were there?

Now consider the same example with this formatting

Person.create(:first_name     => 'Adam',
              :last_name      => 'Smith',
              :occupation     => 'Philosopher',
              :date_of_birth  => '1723-06-23',
              :karma          => 17900717,
              :email          => 'adam.smith@example.com')

The latter example makes it easier to grasp its underlying structure. It is composed one option per line, and the eye and mind is good at estimating the number of lines it perceives. (citation needed)

Had there only been two options, we could have written

Person.create(:first_name => 'Adam', :last_name => 'Smith')

It it nevertheless preferable to use one line per option to facilitate reading and manipulating options

Person.create(:first_name => 'John', #'Adam',
              :last_name  => 'Smith')

Use one item per line when a list of items exceeds 80 characters

From the 80 character per line rule

Good

  attr_accessible :first_name,
                  :last_name,
                  :email,
                  :password,
                  :phone,
                  :address,
                  :city,
                  :password_confirmation,
                  :state,
                  :country

Better

When the ordering of options is equivalent, favor lexicographical order

  attr_accessible :address,
                  :city,
                  :country,
                  :email,
                  :first_name,
                  :last_name,
                  :password,
                  :password_confirmation,
                  :phone,
                  :state

Not as good

It's tempting to place as many options per line as possible. Don't. It makes it a lot more convenient to remove, add, and read options when there is only one per line. Remember, we are not printing screens on paper, and clean code can be read on digital screens.

  attr_accessible :first_name, :last_name, :email, :password,
                  :password_confirmation, :phone, :address, :city, :state,
                  :country

Bad

In this list

  attr_accessible :first_name, :last_name, :email, :password, :password_confirmation, :phone, :address, :city, :state, :country

how many attributes are accessible?

Even worse, perhaps, is multiline over 80 characters

  attr_accessible :first_name, :last_name, :email, :password, :password_confirmation, :phone, :address, :city, :state,
                  :country

Good

In highly indented position, place the first option on the second line

class Reason

  def create
    if person.think?
      Philosopher.create(
        :first_name     => 'Adam',
        :last_name      => 'Smith',
        :occupation     => 'Philosopher',
        :date_of_birth  => '1723-06-23',
        :karma          => 17900717,
        :email          => 'adam.smith@example.com'
      )
    else
      Philosopher.destroy_all
    end
  end

end

Align delimeters vertically on multiline statements

Good

Person.create(:first_name     => 'Adam',
              :last_name      => 'Smith',
              :occupation     => 'Philosopher',
              :date_of_birth  => '1723-06-23',
              :karma          => 17900717,
              :email          => 'adam.smith@example.com')

Bad

Person.create(:first_name => 'Adam',
              :last_name => 'Smith',
              :occupation => 'Philosopher',
              :date_of_birth => '1723-06-23',
              :karma => 17900717,
              :email => 'adam.smith@example.com')

Person.create(:first_name => 'Adam',
            :last_name => 'Smith',
            :occupation => 'Philosopher',
            :date_of_birth => '1723-06-23',
            :karma => 17900717,
            :email => 'adam.smith@example.com')

Bad

Also make sure to left-align options

Person.create(:first_name       => 'Adam', # This option aligns to the left of
                                           # subsequent options
                :last_name      => 'Smith',
                :occupation     => 'Philosopher',
                :date_of_birth  => '1723-06-23',
                :karma          => 17900717,
                :email          => 'adam.smith@example.com')

Leave no whitespace at the end of any line

Good

class Account

  def credit
  end

  def debit
  end

end

Bad

With whitespace represented with a #

class Account

  def credit
  end
##
  def debit
  end

end

Even worse

With whitespace represented with a #

class Account###
##
  def credit######
  end
##
  def debit#
  end#
####
end###
######

Always use 2 space indentation

Good

class Person
  def name
    first_name + ' ' + last_name
  end
end

Bad

Here's an example with 4 space indentation

class Person
    def name
        first_name + ' ' + last_name
    end
end

No tabs, ever

Use spaces around operators

Good

2 + 4
'my' + ' ' + 'space'
@foo ||= 'bar'

Bad

2+4
'my'+' '+'space'
@foo||='bar'

Use spaces after commas

Good

def sum(a, b)
  a + b
end

elements = [1, 2, 3, 21, 45]

Bad

def sum(a,b)
  a + b
end

elements = [1,2,3,21,45]

Use space after colons in 1.9 hash syntax

Good

definition = { awesome: "extremely impressive or daunting" }

Bad

definition = { awesome:"extremely impressive or daunting" }

No semicolons

Good

def sum(a, b)
  a + b
end

Bad

def sum(a, b); a + b; end;

Worse

def sum(a, b);
  a + b;
end;

Use spaces around { and before }

No spaces after ( and before )

Optional spaces after [ and before ]

• Use two spaces before statement modifiers (postfix if/unless/while/until/rescue).

• Indent when as deep as case.

• Use an empty line before the return value of a method (unless it only has one line), and an empty line between defs.

• Use RDoc and its conventions for API documentation. Don't put an empty line between the comment block and the def.

• Use empty lines to break up a long method into logical paragraphs.

Syntax

Use def with parentheses when there are arguments

# Good
def add(user)
  # 'user' is clearly an argument
end

# Bad
def add user
  # It's not clear what 'user' is
end

• Never use for, unless you exactly know why.

• Never use then.

• Use when x; ... for one-line cases.

• 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.)

• Avoid multiline ternary operator (? :), use if.

• Suppress superfluous parentheses when calling methods, but keep them when calling "functions", i.e. when you use the return value in the same line.

  x = Math.sin(y)
  array.delete e

Prefer {...} over do...end

Good

1.upto(10).select { |n| n % 2 == 1 }

Not as good

1.upto(10).select do |n|
  n % 2 == 1
end

Bad

Avoid placing do...end on the same line

1.upto(10).select do |n| n % 2 == 1 end

• Multiline {...} is fine: having different statement endings (} for blocks, end for if/while/...) makes it easier to see what ends where. But use do...end for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs.)

Avoid do...end when chaining

Good

1.upto(10).select { |n| n % 2 == 1 }.map { |n| n * 100 }

Good

It's encouraged to use parentheses when it makes it clearer

1.upto(10).select { |n| (n % 2) == 1 }.map { |n| n * 100 }

Acceptable

It's acceptable to omit the space after { and before }

1.upto(10).select {|n| n % 2 == 1}.map {|n| n * 100}

Not as acceptable

It's not as readable to omit the space before {

1.upto(10).select{|n| n % 2 == 1}.map{|n| n * 100}

Bad

1.upto(10).select do |n| n % 2 == 1 end.map do |n| n * 100 end

Worse

Mixing {...} and do...end when chaining is even worse

1.upto(10).select do |n| n % 2 == 1 end.map { |n| n * 100 }

Avoid return where not required

Good

def tax
  price * tax_rate
end

Bad

def tax
  return price * tax_rate
end

Worse

def tax
  amount = price * tax_rate
  return amount
end

• Avoid line continuation () where not required.

Using the return value of = is acceptable

Good

It is preferable to enclose the expression in parentheses

if (amount = account.outstanding_amount)
  # Do something with 'amount'
end

It is acceptable to omit parentheses when there is a single expression

if amount = account.outstanding_amount
  # Do something with 'amount'
end

Not as good

When there are multiple conditions, using the return value of = doesn't work quite as well

if (amount = account.outstanding_amount) && account.active?
  # Do something with 'amount'
end

Better

It's better to break it down into multiple statments

amount = account.outstanding_amount
if amount && account.active?
  # Do something with 'amount'
end

Use ||= freely

Good

def amount
  # `calculate_amount` is an expensive operation
  @amount ||= calculate_amount
end

Bad

def amount
  # `calculate_amount` is an expensive operation
  calculate_amount
end

• Use non-OO regexps (they won't make the code better). Freely use =, $0-9, $, $` and $' when needed.

Naming

• Use snake_case for methods.

• Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.)

• Use SCREAMING_SNAKE_CASE for other constants.

• The length of an identifier determines its scope. Use one-letter variables for short block/method parameters, according to this scheme:

  • a,b,c: any object

  • d: directory names

  • e: elements of an Enumerable

  • ex: rescued exceptions

  • f: files and file names

  • i,j: indexes

  • k: the key part of a hash entry

  • m: methods

  • o: any object

  • r: return values of short methods

  • s: strings

  • v: any value

  • v: the value part of a hash entry

  • x,y,z: numbers

    And in general, the first letter of the class name if all objects are of that type.

• Use _ or names prefixed with _ for unused variables.

• When using inject with short blocks, name the arguments |a, e| (mnemonic: accumulator, element)

• When defining binary operators, name the argument "other".

• Prefer map over collect, find over detect, find_all over select, size over length.

Comments

• Comments longer than a word are capitalized and use punctuation.

• Avoid superfluous comments.

Spaces after periods

Never use two spaces after a period. If you "think this is wrong", let me Google that for you.

There is one exception to this rule. If you are writing your comments to later be rendered through Markdown, you can use two spaces followed by a line break, to create a line break. Further reading: Markdown syntax.

  # Here's a comment.##
  # I wanted to jump to the next line.

The rest

• Write ruby -w safe code.

• Avoid hashes-as-optional-parameters. Does the method do too much?

• Avoid long methods.

• Avoid long parameter lists.

• Use def self.method to define singleton methods.

• Add "global" methods to Kernel (if you have to) and make them private.

• Avoid alias when alias_method will do.

• Use OptionParser for parsing complex command line options and ruby -s for trivial command line options.

• Write for 1.8, but avoid doing things you know that will break in 1.9.

• Avoid needless metaprogramming.

General

• Code in a functional way, avoid mutation when it makes sense.

• Do not mutate arguments unless that is the purpose of the method.

• Do not mess around in core classes when writing libraries.

• Do not program defensively. (See http://www.erlang.se/doc/programming_rules.shtml#HDR11.)

• Keep the code simple.

• Don't overdesign.

• Don't underdesign.

• Avoid bugs.

• Read other style guides and apply the parts that don't dissent with this list.

• Be consistent.

• Use common sense.

Encoding

Use Unix-style line endings

• Use ASCII (or UTF-8, if you have to)

Credits

Based largely on Christian Neukirchen's Ruby Style Guide.

Contributors

• olauzon
• theIV