A totally unofficial Ruby coding style guide
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README.md

README.md

Abstract

... 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)

This document was created when I, as the Technical Lead of the company which I work for, was asked by the CTO to create some internal documents describing good style and best practices for Ruby programming. I started off by building upon this existing style guide, since I concurred with most of the points in it. I hope it will be useful to other people as well and I hope that I'll get a lot of feedback and suggestions on how to improve the guide for the benefit of the entire Ruby community.

Formatting

  • Use UTF-8 as the source file encoding.

  • Use two space indent, no tabs. (Your editor/IDE should have a setting to help you with that.)

  • Use Unix-style line endings. (Linux/OSX users are covered by default, Windows users have to be extra careful.)

    • If you're using Git you might want to do $ git config --global core.autocrlf true to protect your project from Windows line endings creeping into your project.
  • Use spaces around operators, after commas, colons and semicolons, around { and before } (Exception: Interpolation).

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

    some(arg).other
    [1, 2, 3].length
  • Indent when as deep as case. (As suggested in the Pickaxe.)

    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 one empty line between defs.

    def some_method
      do_something
      do_something_else
      result
    end
    
    def some_method
      result
    end
  • Use RDoc and its conventions for API documentation. (Really RDoc?) Don't put an empty line between the comment block and the def.

  • If you feel you should partition parts of your method with empty lines, consider splitting it into smaller methods before doing so.

  • Do not pollute the file with trailing whitespaces.

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. (Why?)

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

    # bad
    if some_condition then
      # body omitted
    end
    
    # good
    if some_condition
      # body omitted
    end
  • Use &&/|| for boolean expressions, and/or for control flow. The latter pair has low operator precedence

    # boolean expression
    if some_condition && some_other_condition
      do_something
    end
    
    # control flow
    document.saved? or document.save!
  • Avoid multiline ?: (the ternary operator), use if/unless instead.

  • Favor modifier if/unless usage when you have a single-line body.

    # bad
    if some_condition
      do_something
    end
    
    # good
    do_something if some_condition
  • Favor unless over if for negative conditions.

    # bad
    do_something if !some_condition
    
    # good
    do_something unless some_condition
  • Favor unless over if in order to express edge case character (if applicable)

    # bad (if missing address is edge case)
    process address if address.present?
    
    # good (if missing address is edge case)
    process address unless address.blank?
  • Favor unless over if in order to focus on important operations instead of edge case treatment. If edge case treatment is as simple as raising an Exception or returning something, do it directly.

    # bad
    if edge_case
      treat edge_case
    else
      process
    end
    
    # good
    unless edge_case
      process
    else
      treat_edge_case
    end
    
    # good alternative 1
    raise Exception if unprocessable
    process
    
    # good alternative 2
    return nil if unprocessable
    process
  • 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 for single-line blocks. Avoid using {...} for multi-line blocks. 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.

    # bad
    def some_method(some_arr)
      return some_arr.size
    end
    
    # good
    def some_method(some_arr)
      some_arr.size
    end
  • Avoid line continuation (\).

  • Using the return value of = is ok.

    if v = array.grep(/foo/) ...
  • Use ||= freely.

    # set name to Bozhidar, only if it's nil or false
    name ||= "Bozhidar"
  • Make use of blank?, present? and presence.

    # bad
    unless address.nil? || address.empty?
    
    # good
    unless address.blank?
    if address.present?
    
    # bad
    state   = params[:state]   if params[:state].present?
    country = params[:country] if params[:country].present?
    region  = state || country || 'US'
    
    # good
    region = params[:state].presence || params[:country].presence || 'US'
  • Avoid using Perl-style global variables (like $0-9, $`, ...).

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

    # bad
    f (3 + 2) + 1
    
    # good
    f(3 + 2) + 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 question mark. (i.e. Array#empty?).

  • The names of potentially "dangerous" methods (i.e. methods that modify self or the arguments, exit!, etc.) should end with exclamation marks.

  • When defining binary operators, name the argument other.

    def +(other)
      # body omitted
    end
  • Prefer collect over map if you are just collecting attributes without transformations

    # good
    user_names = users.collect { |u| u.name }
    downcased_user_names = user_names.map { |n| n.downcase }

Comments

  • Write self documenting code and ignore the rest of this section. "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)

  • If your comment is a sentence, start it capitalized and use punctuation.

  • Avoid superfluous comments.

    # 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. Try to refactor the code to make it self-explanatory.

Classes

  • Always supply a proper to_s method.
  • Use the attr family of functions to define trivial accessors or mutators.
  • Consider adding factory methods to provide additional sensible ways to create instances of a particular class.
  • Prefer duck-typing over inheritance.
  • Avoid the usage of class (@@) variables due to their "nasty" behavior.
  • Assign methods proper visibility levels (private, protected) in accordance with their intended usage. Don't go off leaving everything public (which is the default).

Exceptions

  • Don't suppress exceptions without sending out a Airbrake notification manually.
  • Avoid rescuing more than you expect to fail (e.g. begin .. rescue - without a specific Exception class)

Misc

  • Avoid methods longer than 10 LOC (lines of code). Ideally most methods will be shorter than 5 LOC.

  • Try to keep the argument list small. Consider the use of opts = {} as last parameter to include further parameters as options.

  • 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
    end
  • Avoid alias when alias_method will do.

  • Write for Ruby 1.9. Don't use legacy Ruby 1.8 constructs.

    • Use the new JavaScript literal hash syntax.

    • Use the new lambda syntax.

    • Methods like inject now accept methods names as arguments.

      [1, 2, 3].inject(:+)
  • Avoid needless metaprogramming.

Design

  • Code in a functional way, avoiding 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 monkey patch them.)
  • Do not program defensively.
  • Keep the code simple and subjective. Each method should have a single, well-defined responsibility.
  • Avoid more than three levels of block nesting.
  • Don't overdesign. Overly complex solutions tend to be brittle and hard to maintain.
  • Don't underdesign. A solution to a problem should be as simple as possible, but no simpler than that. Poor initial design can lead to a lot of problems in the future.
  • Be consistent. In an ideal world, be consistent with these guidelines.
  • Use common sense.

Contributing

Feel free to open tickets or send pull requests with improvements.