These styles are adapted from the excellent work Bozhidar Batsov posted on his Ruby Style Guide project.

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...
Jeffy Coffin

Formatting

• Use UTF-8 as the source file encoding
• Use two-space indent (NO TABS)

• Use Unix style line endings

  Use $git config --global core.autoclrf true to ensure Window’s style doesn’t creep in

• Use spaces around operators, and curly braces (‘{’, ‘}’) after commas and semicolons

sum = 1 + 2
a, b = 1, 2
1 > 2 ? true : false; puts "hi"
[1, 2, 3].each { |e| puts e }

• No spaces after ‘(’, or between braces (‘[’, ‘]’).

some(arg).other
[1, 2, 3].length

• Indent when as deep as case.

case
when song.name == 'Tik Tok'
  puts "Not again!"
when song.duration > 120
  puts "That's really long"
when Time.now.hour > 21
  puts "It's time to start coding"
else
  song.play
end

epoch = case year
        when 1607..1777 then "Colonial Period"
        when 1778..1812 then "Early Republic"

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

def some_method
  do_something
  do_something_else

  result
end

def do_something
  result
end

• Use RDoc and its conventions for documentation (SDoc may be used to generate more searchable documentation).
• Use empty lines to break up a method in to logical paragraphs.
• Keep lines to fewer than 80 characters.

Syntax

• Use def with parentheses when there are arguments. Omit parentheses when the method does not accept any arguments

def some_method
  # payload
end

def method_with_arguments(arg1, arg2)
  # payload
end

• Never use for, unleass you know exactly why. Iterators should be used instead

arr = [1, 2, 3]

# bad
for elem in arr do
  puts elem
end

# good
array.each { |elem| puts elem }

• Never use then for multi-line if/unless

# bad
if some_condition then
  # payload
end

# good
if some_condition
  # payload
end

• Favor ther ternary operator over if/then/else/end constructs. It’s more common and 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

• Use && and || for boolean expressions. Use and and or for flow control.

# boolean expression
if some_condition && some_other_condition
  do_something
end

# control flow
document.saved? or document.save!

• Avoid multi-line ternary operations, 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

# another good option
some_condition and do_something

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

# bad
do_something if !some_condition

# good
do_something unless some_condition

# another good option
some_condition or do_something

• 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 (\) 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 = is ok.

if v = array.grep(/foo/) ...

• Use

  = freely.

# set name to Bozhidar, only if it's nil or false
name ||= "Bozhidar"

• Avoid using Perl-style special variables (like $0-9, $`, …).

• 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

• 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 in inheritance.
• 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.

Exceptions

• Don’t suppress exceptions.
• Don’t use exceptions for flow of control.
• Avoid rescuing the Exception class.

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.
• 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

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/(.*)$)

• Avoid %q, %Q, %x, %s, and %W.

• Prefer () as delimiters for all % literals.

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.
• 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

• 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.
• 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 method names as arguments.

  [1, 2, 3].inject(:+)

• Avoid needless metaprogramming.

Design

• Use common sense.
• Code in a functional way, avoiding mutation when that 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 (although this is 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.