The Redbet Ruby Style Guide

Forked from https://github.com/bbatsov/ruby-style-guide

Table of Contents

• Source Code Layout
• Syntax
• Naming
• Comments
• Annotations
• Classes
• Exceptions
• Collections
• Strings
• Regular Expressions
• Percent Literals
• Metaprogramming
• Misc

Source Code Layout

• Use UTF-8 as the source file encoding.

• Use two spaces per indentation level.

• 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.

  The only exception is when using the exponent operator:

  e = M * c**2

• No spaces after (, [ or before ], ).

• 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
    data = initialize(options)
  
    data.manipulate!
  
    data.result
  end
  
  def some_method
    result
  end

• Align the parameters of a method call if they span over multiple lines.

  # bad starting point (line is too long)
  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

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

• Keep lines fewer than 80 characters.

• Avoid trailing whitespace.

Syntax

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

• 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.

• Never use then for multi-line if/unless.

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

• 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.

• Never use if x: ... - it is removed in Ruby 1.9. Use the ternary operator instead.

• 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 and/or if precedence allows, else fall back to &&/||

• 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.

• Favor unless over if for negative conditions (or control flow or).

• Never use unless with else. Rewrite these with the positive case first.

• Don't use parentheses around the condition of an if/unless/while, unless the condition contains an assignment (see "Using the return value of =" below).

• Favor modifier while/until usage when you have a single-line body.

• Favor until over while for negative conditions.

• Omit parentheses around parameters for methods where it makes sense.

• 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.

• Avoid return where not required.

• Do not use spaces around the = operator when assigning default values to method parameters

• Use line continuation (\) sparingly

• Use ||= freely to initialize variables.

• Don't use ||= to initialize boolean variables. (False values would be set to true)

• Never put a space between a method name and the opening parenthesis.

• 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.

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

• Use _ for unused block parameters.

  # bad
  result = hash.map { |k, v| v + 1 }
  
  # good
  result = hash.map { |_, v| v + 1 }

Naming

• 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.
• 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.
• Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.
• When using reduce with short blocks, name the arguments |a, e| (accumulator, element).
• When defining binary operators, name the argument other.
• Prefer map over collect, find over detect, select over find_all, reduce over inject and size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use of select is encouraged over find_all is that it goes together nicely with reject and its name is pretty self-explanatory.

Comments

• 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. An outdated is worse than no comment at all.

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

• Avoid writing comments that states something is wrong but gives no additional information. Specify instead what should have been done, or better yet, do it!

  # bad
  # TODO: aaah ugly, delete me, I do not belong here
  def generic_method
  
  # good
  # TODO: Method should be moved to namespace A, this will
  # break lots of tests though and I dont have time now.
  def generic_method

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.

• If multiple lines are required to describe the problem, subsequent lines should be indented two spaces after the #.

  def bar
    # FIXME: This has crashed occasionally since v3.2.1. It may
    #   be related to the BarBazUtil upgrade.
    baz(:quux)
  end

• In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

  def bar
    sleep 100 # OPTIMIZE
  end

• Use TODO to note missing features or functionality that should be added at a later date.

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

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

• Use HACK to note code smells where questionable coding practices were used and should be refactored away.

• Use REVIEW to note anything that should be looked at to confirm it is working as intended. For example: REVIEW: Are we sure this is how the client does X currently?

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

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
  class Person < Struct.new (:first_name, :last_name)
  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).

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

  class SomeClass
    def public_method
      # ...
    end
  
    private
  
    def private_method
      # ...
    end
  end

• Use def self.method to define singleton methods instead of using the class/module name. This makes the methods more resistant to refactoring changes.

Exceptions

• Signal exceptions using the fail keyword. Use raise only when catching an exception and re-raising it (because here you're not failing, but explicitly and purposefully raising an exception).

  begin
    fail 'Oops';
  rescue => error
    raise if error.message != 'Oops'
  end

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

  def foo
    begin
      fail
    ensure
      return 'very bad idea'
    end
  end

• Use implicit begin blocks 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

• Avoid rescuing the Exception class. This will trap signals and calls to exit, requiring you to kill -9 the process.

  # bad
  begin
    # calls to exit and kill signals will be caught (except kill -9)
    exit
  rescue Exception
    puts "you didn't really want to exit, right?"
    # exception handling
  end
  
  # good
  begin
    # a blind rescue rescues from StandardError, not Exception as many
    # programmers assume.
  rescue => e
    # exception handling
  end
  
  # also good
  begin
    # an exception occurs here
  
  rescue StandardError => e
    # exception handling
  end

• Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from.

  # bad
  begin
    # some code
  rescue Exception => e
    # some handling
  rescue StandardError => e
    # some handling
  end
  
  # good
  begin
    # some code
  rescue StandardError => e
    # some handling
  rescue Exception => e
    # some handling
  end

• Release external resources obtained by your program in an ensure block.

  f = File.open('testfile')
  begin
    # .. process
  rescue
    # .. handle error
  ensure
    f.close unless f.nil?
  end

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 = {}

• Prefer %w to the literal array syntax when you need an array of strings.

  # bad
  STATES = ['draft', 'open', 'closed']
  
  # good
  STATES = %w(draft open closed)

• 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.

• Avoid the use of mutable object as hash keys.

• 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'

• Don't use {} around instance 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
    def to_s
      "#{@first_name} #{@last_name}"
    end
  
    # good
    def to_s
      "#@first_name #@last_name"
    end
  end

• 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

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.

  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.

  /(first|second)/   # bad
  /(?:first|second)/ # good

• Avoid using $1-9 as it can be hard to track what they contain. Named groups can be used instead.

  # bad
  /(regexp)/ =~ string
  ...
  process $1
  
  # good
  /(?<meaningful_var>regexp)/ =~ string
  ...
  process meaningful_var

• Character classes have only 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.

Percent Literals

• Use %w freely.

  STATES = %w(draft open closed)

• Use %() 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>)

• Use %r only for regular expressions matching more than one '/' character.

  # bad
  %r(\s+)
  
  # still bad
  %r(^/(.*)$)
  # should be /^\/(.*)$/
  
  # good
  %r(^/blog/2011/(.*)$)

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, unless dealing with defined constants.

  • 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 to class_eval{ def ... }

• When using class_eval (or other eval) with string interpolation, add a comment block showing its appearance if interpolated (a practice I learned from the rails code):

  # from activesupport/lib/active_support/core_ext/string/output_safety.rb
  UNSAFE_STRING_METHODS.each do |unsafe_method|
    if 'String'.respond_to?(unsafe_method)
      class_eval <<-EOT, __FILE__, __LINE__ + 1
        def #{unsafe_method}(*args, &block)       # def capitalize(*args, &block)
          to_str.#{unsafe_method}(*args, &block)  #   to_str.capitalize(*args, &block)
        end                                       # end
  
        def #{unsafe_method}!(*args)              # def capitalize!(*args)
          @dirty = true                           #   @dirty = true
          super                                   #   super
        end                                       # end
      EOT
    end
  end

• avoid using method_missing for metaprogramming. Backtraces become messy; the behavior is not listed in #methods; misspelled method calls might silently work (nukes.launch_state = false). Consider using delegation, proxy, or define_method instead. If you must, use method_missing,

  • be sure to also define respond_to?

  • 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

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

• Avoid alias when alias_method will do.

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

• Code in a functional way, avoiding mutation when that makes sense.

• 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.