A community-driven Ruby coding style guide
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README.md

README.md

Prelude

Style is what separates the good from the great.
-- Bozhidar Batsov

One thing has always bothered me as Ruby developer - Python developers have a great programming style reference (PEP-8) and we never got an official guide, documenting Ruby coding style and best practices. And I do believe that style matters. I also believe that such fine fellows, like us Ruby developers, should be quite capable to produce this coveted document.

This guide started its life as our internal company Ruby coding guidelines (written by yours truly). At some point I decided that the work I was doing might be interesting to members of the Ruby community in general and that the world had little need for another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.

Since the inception of the guide I've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.

By the way, if you're into Rails you might want to check out the complementary Ruby on Rails 3 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. I've tried to add the rationale behind the rules (if it's omitted I've assumed that is pretty obvious).

I didn't come up with all the rules out of nowhere - they are mostly based on my extensive career as a professional software engineer, feedback and suggestions from members of the Ruby community and various highly regarded Ruby programming resources, such as "Programming Ruby 1.9" and "The Ruby Programming Language".

The guide is still a work in progress - some rules are lacking examples, some rules don't have examples that illustrate them clearly enough. In due time these issues will be addressed - just keep them in mind for now.

You can generate a PDF or an HTML copy of this guide using Transmuter.

Table of Contents

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...
-- Jerry Coffin (on indentation)

  • Use UTF-8 as the source file encoding.

  • Use two spaces per indentation level.

    # 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, around { and before }. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code.

    sum = 1 + 2
    a, b = 1, 2
    1 > 2 ? true : false; puts 'Hi'
    [1, 2, 3].each { |e| puts e }
  • No spaces after (, [ or before ], ).

    some(arg).other
    [1, 2, 3].length
  • Indent when as deep as case. I know that many would disagree with this one, but it's the style established in both the "The Ruby Programming Language" and "Programming Ruby".

    case
    when song.name == 'Misty'
      puts 'Not again!'
    when song.duration > 120
      puts 'Too long!'
    when Time.now.hour > 21
      puts "It's too late"
    else
      song.play
    end
    
    kind = case year
           when 1850..1889 then 'Blues'
           when 1890..1909 then 'Ragtime'
           when 1910..1929 then 'New Orleans Jazz'
           when 1930..1939 then 'Swing'
           when 1940..1950 then 'Bebop'
           else 'Jazz'
           end
  • Use empty lines between defs and to break up a method into logical paragraphs.

    def some_method
      something = find_something(1)
      something_else = find_something_else(2)
    
      first = something.manipulate!
      second = something_else.frobnicate
    
      first + second
    end
    
    def some_method
      result
    end

    When methods are short (say, less than 3 lines, or when each "paragraph" is only one line), then it's ok to omit the blank lines. This is common in simple specs:

    describe User do
      it "should be wibblable" do
        user = User.find(1)
        user.wibble
        user.should be_wibbled
      end
    end

    The objective is to have all lines in a "paragraph" to have the same weight.

  • Leave an empty line after if..end if the method continues. Never leave more than one empty line.

    # bad
    def some_method
      if condition
        puts "Yep!"
      else
        puts "Nope!"
      end
      if something_else
        puts "Yep!"
      else
        puts "Nope!"
      end
      puts "Done!"
    end
    
    # good
    def some_method
      if condition
        puts "Yep!"
      else
        puts "Nope!"
      end
    
      if something_else
        puts "Yep!"
      else
        puts "Nope!"
      end
    
      puts "Done!"
    end
    
  • Do not leave empty lines after a class definition or between ends

    # bad
    class Foo
    
      def bar
        puts "Bar"
      end
    
    end
    
    # good
    class Foo
      def bar
        puts "Bar"
      end
    end
    
  • Align the parameters of a method call if they span over multiple lines.

    # starting point (line is too long)
    def send_mail(source)
      Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text)
    end
    
    # bad (double indent)
    def send_mail(source)
      Mailer.deliver(
          to: 'bob@example.com',
          from: 'us@example.com',
          subject: 'Important message',
          body: source.text)
    end
    
    # better
    def send_mail(source)
      Mailer.deliver(to: 'bob@example.com',
                     from: 'us@example.com',
                     subject: 'Important message',
                     body: source.text)
    end
    
    # best
    def send_mail(source)
      Mailer.deliver(
        to: 'bob@example.com',
        from: 'us@example.com',
        subject: 'Important message',
        body: source.text
      )
    end
  • Keep lines fewer than 80 characters.

  • Avoid trailing whitespace (Remember whitespace)

Syntax

  • Use def with parentheses when there are arguments. Omit the parentheses when the method doesn't accept any arguments.

    def some_method
      # body omitted
    end
    
    def some_method_with_arguments(arg1, arg2)
      # body omitted
    end
  • Never use for, unless you know exactly why. Most of the time iterators should be used instead. for is implemented in terms of each (so you're adding a level of indirection), but with a twist - for doesn't introduce a new scope (unlike each) and variables defined in its block will be visible outside it.

    arr = [1, 2, 3]
    
    # bad
    for elem in arr do
      puts elem
    end
    
    # good
    arr.each { |elem| puts elem }
  • Never use then for multi-line if/unless.

    # bad
    if some_condition then
      # body omitted
    end
    
    # good
    if some_condition
      # body omitted
    end
  • Favor the ternary operator(?:) over if/then/else/end constructs. It's more common and obviously more concise.

    # bad
    result = if some_condition then something else something_else end
    
    # good
    result = some_condition ? something : something_else
  • Use one expression per branch in a ternary operator. This also means that ternary operators must not be nested. Prefer if/else constructs in these cases.

    # bad
    some_condition ? (nested_condition ? nested_something : nested_something_else) : something_else
    
    # good
    if some_condition
      nested_condition ? nested_something : nested_something_else
    else
      something_else
    end
  • Never use if x: ... - it is removed in Ruby 1.9. Use the ternary operator instead.

    # bad
    result = if some_condition: something else something_else end
    
    # good
    result = some_condition ? something : something_else
  • Never use if x; .... Use the ternary operator instead.

  • Use when x then ... for one-line cases. The alternative syntax when x: ... 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.)

    # boolean expression
    if some_condition && some_other_condition
      do_something
    end
    
    # control flow
    document.saved? or document.save!
  • Avoid multi-line ?: (the ternary operator), use if/unless instead. If you really must use a multi-line ternary expression, line up the ? and :

      some_condition_is_true ?
                do_something :
                do_something_else
  • Favor modifier if/unless usage when you have a single-line body. Another good alternative is the usage of control flow and/or.

    # bad
    if some_condition
      do_something
    end
    
    # good
    do_something if some_condition
    
    # another good option
    some_condition and do_something
  • When choosing between unless and if, favor the most natural sounding.

    # good
    do_something unless error
    
    # bad
    do_something if !error
    
    # good
    spew if !successful
    
    # bad - unless you expect your code to fail
    spew unless successful
  • Never use unless with else. Rewrite these with the positive case first.

    # bad
    unless success?
      puts 'failure'
    else
      puts 'success'
    end
    
    # good
    if success?
      puts 'success'
    else
      puts 'failure'
    end
  • Don't use parentheses around the condition of an if/unless/while

    # bad
    if (x > 10)
      # body omitted
    end
    
    # good
    if x > 10
      # body omitted
    end
    
    The one exception is when the condition contains an assignment, to
    signify intent:
    
    # bad - should this have been a '=='?
    if x = self.next_value
      # body omitted
    end
    
    # good
    if (x = self.next_value)
      # body omitted
    end
  • Favor until over while for negative conditions.

    # bad
    do_something while !some_condition
    
    # good
    do_something until some_condition
  • Omit parentheses around parameters for methods that are part of an internal DSL (e.g. Rake, Rails, RSpec), methods that are with "keyword" status in Ruby (e.g. attr_reader, puts) and attribute access methods. Use parentheses around the arguments of all other method invocations.

    class Person
      attr_reader :name, :age
    
      # omitted
    end
    
    temperance = Person.new('Temperance', 30)
    temperance.name
    
    puts temperance.age
    
    x = Math.sin(y)
    array.delete(e)
  • 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).

    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 }
    
  • Avoid return where not required.

    # bad
    def some_method(some_arr)
      return some_arr.size
    end
    
    # good
    def some_method(some_arr)
      some_arr.size
    end
  • Prefer tap when returning an object from a method chain

    # bad
    def some_method
      foo = Foo.new
      foo.bar = "Bar"
      foo.baz = "Baz"
    
      foo
    end
    
    # good
    def some_method
      Foo.new.tap do |f|
        f.bar = "Bar"
        f.baz = "Baz"
      end
    end

    However note that for some classes, like ActiveModel subclasses, the instance is yielded to the initializer making the #tap unnecessary.

    def some_method
      User.new do |user|
        user.bar = "Bar"
        user.baz = "Baz"
      end
    end
  • Avoid self where not required.

    # bad
    def ready?
      if self.last_reviewed_at > self.last_updated_at
        self.worker.update(self.content, self.options)
        self.status = :in_progress
      end
      self.status == :verified
    end
    
    # good
    def ready?
      if last_reviewed_at > last_updated_at
        worker.update(content, options)
        self.status = :in_progress
      end
      status == :verified
    end
  • As a corollary, avoid shadowing methods with local variables unless they are both equivalent

    class Foo
      attr_accessor :options
    
      # ok
      def initialize(options)
        self.options = options
        # both options and self.options are equivalent here
      end
    
      # bad
      def do_something(options = {})
        unless options[:when] == :later
          output(self.options[:message])
        end
      end
    
      # good
      def do_something(params = {})
        unless params[:when] == :later
          output(options[:message])
        end
      end
    end
    
  • Use spaces around the = operator when assigning default values to method parameters:

    # bad
    def some_method(arg1=:default, arg2=nil, arg3=[])
      # do something...
    end
    
    # good
    def some_method(arg1 = :default, arg2 = nil, arg3 = [])
      # do something...
    end

    While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).

  • Avoid line continuation (\) where not required. In practice, avoid using line continuations at all.

    # bad
    result = 1 - \
             2
    
    # good (but still ugly as hell)
    result = 1 \
             - 2
  • Using the return value of = (an assignment) is ok, but surround the assignment with parenthesis if intent is not obvious.

    # good - shows intended use of assignment
    if (v = array.grep(/foo/)) ...
    
    # bad
    if v = array.grep(/foo/) ...
    
    # also good - shows intended use of assignment and has correct precedence.
    if (v = self.next_value) == 'hello' ...
  • Use ||= freely to initialize variables.

    # set name to Bozhidar, only if it's nil or false
    name ||= 'Bozhidar'
  • Don't use ||= to initialize boolean variables. (Consider what would happen if the current value happened to be false.)

    # bad - would set enabled to true even if it was false
    enabled ||= true
    
    # good
    enabled = true if enabled.nil?
  • 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).

  • When the keys of your hash are symbols use the Ruby 1.9 hash literal syntax.

    # bad
    hash = { :one => 1, :two => 2 }
    
    # good
    hash = { one: 1, two: 2 }
  • Use the new lambda literal syntax.

    # bad
    lambda = lambda { |a, b| a + b }
    lambda.call(1, 2)
    
    # good
    lambda = ->(a, b) { a + b }
    lambda.(1, 2)

Naming

The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton

  • Use snake_case for methods and variables.

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

  • Use SCREAMING_SNAKE_CASE for other constants.

  • Don't use short (1 or 2 char) variable names unless it's a parameter of a single-line block:

    # ok
    open(path) { |f| puts f.line }
    
    # also ok
    open(path) { |file| puts file.line }
    
    # bad
    open(path) do |f|
      # ...
    end
    
    # good
    open(path) do |file|
      # ...
    end
  • Never shorten names by simply omitting a few letters (e.g. search, not srch; response, not res).

  • Only abbreviate if the name is extremely long - learn how to autocomplete long names with your editor! If you must abbreviate, favor generalizing the noun over using initials (e.g., shorten user_search to search, not us).

  • Phrasal verbs (methods) are two words, while their noun (variable) counterparts are typically one. So log_in and set_up are method names, while login and setup are variable names.

  • Never use the object's type as a variable name (e.g hash or h). There is almost certainly a better, more descriptive name.

  • The names of predicate methods (methods that return a boolean value) should end in a question mark. (i.e. Array#empty?).

  • The names of potentially "dangerous" methods (i.e. methods that modify self or the arguments, exit! (doesn't run the finalizers like exit does), etc.) should end with an exclamation mark if there exists a safe version of that dangerous method.

    # bad - there is not matching 'safe' method
    class Person
      def update!
      end
    end
    
    # good
    class Person
      def update
      end
    end
    
    # good
    class Person
      def update!
      end
    
      def update
      end
    end
  • Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.

    class Array
      def flatten_once!
        res = []
    
        each do |e|
          [*e].each { |f| res << f }
        end
    
        replace(res)
      end
    
      def flatten_once
        dup.flatten_once!
      end
    end

    This does not apply if the bang signifies exception throwing. In this case, the bang version should be defined in terms of the non-bang one:

    class Thing
      def save!
        save or
          raise Invalid.new(self)
      end
    end
  • Avoid "flag" parameters - write a separate method or take an options hash instead.

    # bad
    def offers(reload = false)
      self.reload if reload
      # ...
    end
    
    # better
    def offers(options = {})
      self.reload if options[:reload]
      # ...
    end
    
    # better
    def reload_with_offers
      self.reload
      offers
    end
    
    # best: don't conflate two unrelated actions into one method!
  • Prefer attributes or parameters to options for a final hash parameter if it's not truly optional. A parameter named options should always have a default.

    # bad
    def foo(options)
    end
    
    # good
    def foo(options = {})
    end
    
    # good
    def foo(parameters)
    end
  • When using reduce with short blocks, name the arguments |a, e| (accumulator, element).

  • When defining binary operators, name the argument other.

    def +(other)
      # body omitted
    end
  • Prefer map over collect, find over detect, select over find_all, inject over reduce and size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use of select is encouraged over find_all is that it goes together nicely with reject and its name is pretty self-explanatory.

Comments

Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?" Improve the code and then document it to make it even clearer.
-- Steve McConnell

  • Write self-documenting code and ignore the rest of this section. Seriously!

  • Comments longer than a word are capitalized and use punctuation. Use one space after periods.

  • Avoid superfluous comments.

    # bad
    counter += 1 # increments counter by one
  • Keep existing comments up-to-date. Favor explanatory commit messages instead. An outdated comment is worse than no comment at all.

Good code is like a good joke - it needs no explanation.
-- Russ Olsen

  • Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory. (Do or do not - there is no try. --Yoda)

  • Never push commented out code to master.

Annotations

  • Annotations should usually be written on the line immediately above the relevant code.

  • The annotation keyword is followed by a colon and a space, then a note describing the problem.

    def bar
      # FIXME: This has crashed occasionally since v3.2.1. It may
      #   be related to the BarBazUtil upgrade.
      baz(:quux)
    end
  • In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

    def bar
      sleep 100 # OPTIMIZE
    end
  • Use TODO to note missing features or functionality that should be added at a later date.

  • Use FIXME to note broken code that needs to be fixed.

  • Use OPTIMIZE to note slow or inefficient code that may cause performance problems.

  • Use other custom annotation keywords if it feels appropriate, but be sure to document them in your project's README or similar.

Classes

  • 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
  • Consider using Struct.new, which defines the trivial accessors, constructor and comparison operators for you.

    # good
    class Person
      attr_reader :first_name, :last_name
    
      def initialize(first_name, last_name)
        @first_name = first_name
        @last_name = last_name
      end
    end
    
    # better
    Person = Struct.new(:first_name, :last_name) do
    end
  • Consider adding factory methods to provide additional sensible ways to create instances of a particular class.

    class Person
      def self.create(options_hash)
        # body omitted
      end
    end
  • Prefer duck-typing over inheritance.

    # bad
    class Animal
      # abstract method
      def speak
      end
    end
    
    # extend superclass
    class Duck < Animal
      def speak
        puts 'Quack! Quack'
      end
    end
    
    # extend superclass
    class Dog < Animal
      def speak
        puts 'Bau! Bau!'
      end
    end
    
    # good
    class Duck
      def speak
        puts 'Quack! Quack'
      end
    end
    
    class Dog
      def speak
        puts 'Bau! Bau!'
      end
    end
  • Avoid the usage of class (@@) variables due to their "nasty" behavior in inheritance.

    class Parent
      @@class_var = 'parent'
    
      def self.print_class_var
        puts @@class_var
      end
    end
    
    class Child < Parent
      @@class_var = 'child'
    end
    
    Parent.print_class_var # => will print "child"

    As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.

  • Assign proper visibility levels to methods (private, protected) in accordance with their intended usage. Don't go off leaving everything public (which is the default). After all we're coding in Ruby now, not in Python.

  • Indent the public, protected, and private methods as much the method definitions they apply to. Leave one blank line above and below them.

    class SomeClass
      def public_method
        # ...
      end
    
      private
    
      def private_method
        # ...
      end
    end
    
  • Use def self.method to define singleton methods. This makes the methods more resistant to refactoring changes.

    class TestClass
      # bad
      def TestClass.some_method
        # body omitted
      end
    
      # good
      def self.some_other_method
        # body omitted
      end
    
      # Also possible and convenient when you
      # have to define many singleton methods.
      class << self
        def first_method
          # body omitted
        end
    
        def second_method_etc
          # body omitted
        end
      end
    end

Exceptions

  • Never return from an ensure block. If you explicitly return from a method inside an ensure block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised at all. In effect, the exception will be silently thrown away.

    def foo
      begin
        fail
      ensure
        return 'very bad idea'
      end
    end
  • Use implicit begin blocks when possible.

    # bad
    def foo
      begin
        # main logic goes here
      rescue
        # failure handling goes here
      end
    end
    
    # good
    def foo
      # main logic goes here
    rescue
      # failure handling goes here
    end
  • Mitigate the proliferation of begin blocks via the use of 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
      # 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
  • 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
  • Always specify which exception classes to rescue, and rescue the most specific exception class possible (unless you're reraising).

    # horrible
    begin
      # ...
    rescue Exception
      # This could be absolutely anything, including an Interrupt,
      # NoMemoryError, or SystemStackError. Probably don't want that.
    end
    
    # bad
    begin
      # ...
    rescue => e
      # Rescues StandardError, but more likely the programmer was just
      # negligent and didn't care.
    end
    
    # good
    begin
      # ...
    rescue Timeout::Error => e
      # ...
    end
  • Never use the rescue statement modifier, as there is no way to specify which exception classes to rescue.

    # bad
    do_something rescue nil
    
    # good
    begin
      do_something
    rescue SomeException
      # ...
    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.

Collections

  • Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).

    # bad
    arr = Array.new
    hash = Hash.new
    
    # good
    arr = []
    hash = {}
  • Avoid the creation of huge gaps in arrays.

    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.

    # 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.

    # 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.

Strings

  • Prefer string interpolation instead of string concatenation:

    # bad
    email_with_name = user.name + ' <' + user.email + '>'
    
    # good
    email_with_name = "#{user.name} <#{user.email}>"
  • Prefer single-quoted strings when you don't need string interpolation or special symbols such as \t, \n, ', etc.

    # bad
    name = "Bozhidar"
    
    # good
    name = 'Bozhidar'
  • Avoid using String#+ when you need to construct large data chunks. Instead, use String#<<. Concatenation mutates the string instance in-place and is always faster than String#+, which creates a bunch of new string objects.

    # good and also fast
    html = ''
    html << '<h1>Page title</h1>'
    
    paragraphs.each do |paragraph|
      html << "<p>#{paragraph}</p>"
    end

Metaprogramming

  • Do not mess around in core classes when writing libraries. (Do not monkey patch them.) In application code, a small amount is acceptable, provided the changes are truly globally applicable.

  • Monkey patch library classes as a last resort, and only to fix library bugs. Send those patches upstream, and include the URL of the pull request in a comment above the monkey patch, so it may one day be removed.

  • When defining dynamic methods, prefer the string-interpolated form of class_eval for performance reasons. Always specify file and line numbers so backtraces make sense. Note that if a heredoc is used, the correct line number is __LINE__ + 1.

    class_eval <<-EOS, __FILE__, __LINE__ + 1
      def #{method}
      end
    end
  • Avoid using method_missing if possible. Performance sucks; backtraces become messy; and the behavior is not listed in #methods.

  • If you must use method_missing:

    • 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

    • delegate to assertive, non-magical methods:

      # bad
      def method_missing(meth, *args, &block)
        if method =~ /\Afind_by_(?<prop>.*)/
          # ... lots of code to do a find_by
        else
          super
        end
      end
      
      # better
      def method_missing(meth, *args, &block)
        if meth =~ /\Afind_by_(?<prop>.*)/
          find_by(prop, *args, &block)
        else
          super
        end
      end

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.

    #bad
    $foo_bar = 1
    
    #good
    class Foo
      class << self
        attr_accessor :bar
      end
    end
    
    Foo.bar = 1
  • Use OptionParser for parsing complex command line options and ruby -s for trivial command line options.

  • Don't use File.join to piece together file names from static strings.

    # bad
    path = File.join(Rails.root, 'config', 'blah.yml')
    
    # good
    path = "#{Rails.root}/config/blah.yml"
    
    # good - works because Rails.root is a Pathname
    path = Rails.root.join('config/blah.yml')

    (Contrary to popular belief, this runs just fine on Windows.)

  • 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.

Contributing

Nothing written in this guide is set in stone. It's my desire to work together with everyone interested in Ruby coding style, so that we could ultimately create a resource that will be beneficial to the entire Ruby community.

Feel free to open tickets or send pull requests with improvements. Thanks in advance for your help!

Spread the Word

A community-driven style guide is of little use to a community that doesn't know about its existence. Tweet about the guide, share it with your friends and colleagues. Every comment, suggestion or opinion we get makes the guide just a little bit better. And we want to have the best possible guide, don't we?