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.

  # gooddefsome_methoddo_somethingend# bad - four spacesdefsome_methoddo_somethingend

• 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 + 2a,b=1,21 > 2 ? true : false;puts'Hi'[1,2,3].each{ |e| putse}

  The only exception is when using the exponent operator:

  # bade=M * c ** 2# goode=M * c**2

• 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".

  casewhensong.name == 'Misty'puts'Not again!'whensong.duration > 120puts'Too long!'whenTime.now.hour > 21puts"It's too late"elsesong.playendkind=caseyearwhen1850..1889then'Blues'when1890..1909then'Ragtime'when1910..1929then'New Orleans Jazz'when1930..1939then'Swing'when1940..1950then'Bebop'else'Jazz'end

• Use empty lines between defs and to break up a method into logical paragraphs.

  defsome_methoddata=initialize(options)data.manipulate!data.resultenddefsome_methodresultend

• 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.

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

  defsome_method# body omittedenddefsome_method_with_arguments(arg1,arg2)# body omittedend

• 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]# badforeleminarrdoputselemend# goodarr.each{ |elem| putselem}

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

  # badifsome_conditionthen# body omittedend# goodifsome_condition# body omittedend

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

  # badresult=ifsome_conditionthensomethingelsesomething_elseend# goodresult=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.

  # badsome_condition ? (nested_condition ? nested_something : nested_something_else) : something_else# goodifsome_conditionnested_condition ? nested_something : nested_something_elseelsesomething_elseend

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

  # badresult=ifsome_condition: somethingelsesomething_elseend# goodresult=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 expressionifsome_condition && some_other_conditiondo_somethingend# control flowdocument.saved?ordocument.save!

• 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.

  # badifsome_conditiondo_somethingend# gooddo_somethingifsome_condition# another good optionsome_conditionanddo_something

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

  # baddo_somethingif !some_condition# gooddo_somethingunlesssome_condition# another good optionsome_conditionordo_something

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

  # badunlesssuccess?puts'failure'elseputs'success'end# goodifsuccess?puts'success'elseputs'failure'end

• Don't use parentheses around the condition of an if/unless/while.

  # badif(x > 10)# body omittedend# goodifx > 10# body omittedend

• 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.

  classPersonattr_readername,age# omittedendtemperance=Person.new('Temperance',30)temperance.nameputstemperance.agex=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). Avoid do...end when chaining.

  names=["Bozhidar","Steve","Sarah"]# goodnames.each{ |name| putsname}# badnames.eachdo |name| putsnameend# goodnames.select{ |name| name.start_with?("S")}.map{ |name| name.upcase}# badnames.selectdo |name| name.start_with?("S")end.map{ |name| name.upcase}

  Some will argue that multiline chaining would look OK with the use of{...}, but they should ask themselves - it this code really readable and can't the blocks contents be extracted into nifty methods.

• Avoid return where not required.

  # baddefsome_method(some_arr)returnsome_arr.sizeend# gooddefsome_method(some_arr)some_arr.sizeend

• Use spaces around the = operator when assigning default values to method parameters:

  # baddefsome_method(arg1=:default,arg2=nil,arg3=[])# do something...end# gooddefsome_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.

  # badresult=1 - \ 2# good (but still ugly as hell)result=1 \ - 2

• Using the return value of = (an assignment) is ok.

  ifv=array.grep(/foo/) ...

• Use ||= freely to initialize variables.

  # set name to Bozhidar, only if it's nil or falsename ||= '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 falseenabled ||= true# goodenabled=trueifenabled.nil?

• Avoid using Perl-style special variables (like $0-9, `$``, etc. ). They are quite cryptic and their use in anything but one-liner scripts is discouraged.

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

  # badf(3 + 2) + 1# goodf(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).

• Always run the Ruby interpreter with the -w option so it will warn you if you forget either of the rules above!

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.

• 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!, etc.) should end with an exclamation mark.

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

• When defining binary operators, name the argument other.

  def +(other)# body omittedend

• Prefer map over collect, find over detect, select over find_all, size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it.

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

• 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 #.

  defbar# 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.

  defbarsleep100# OPTIMIZEend

• 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.

• Always supply a proper to_s method.

  classPersonattr_reader:first_name,:last_namedefinitialize(first_name,last_name)@first_name=first_name@last_name=last_nameenddefto_s"#@first_name #@last_name"endend

• 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.

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

  classSomeClassdefpublic_method# ...endprivatedefprivate_method# ...endend

• Use def self.method to define singleton methods. This makes the methods more resistant to refactoring changes.

  classTestClass# baddefTestClass.some_method# body omittedend# gooddefself.some_other_method# body omittedend# Also possible and convenient when you# have to define many singleton methods.class << selfdeffirst_method# body omittedenddefsecond_method_etc# body omittedendendend

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

• It's ok to use arrays as sets for a small number of elements.
• Prefer %w to the literal array syntax when you need an array of strings.
• Avoid the creation of huge gaps in arrays.
• Use Set instead of Array when dealing with lots of elements.
• Use symbols instead of strings as hash keys.
• Avoid the use of mutable object as hash keys.
• Use the new 1.9 literal hash syntax in preference to the hashrocket syntax.
• Rely on the fact that hashes in 1.9 are ordered.
• Never modify a collection while traversing it.

• Prefer string interpolation instead of string concatenation:

  # bademail_with_name=user.name + ' <' + user.email + '>'# goodemail_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.

  # badname="Bozhidar"# goodname='Bozhidar'

• Don't use {} around instance variables being interpolated into a string.

  classPersonattr_reader:first_name,:last_namedefinitialize(first_name,last_name)@first_name=first_name@last_name=last_nameend# baddefto_s"#{@first_name}#{@last_name}"end# gooddefto_s"#@first_name #@last_name"endend

• 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 fasthtml=''html << '<h1>Page title</h1>'paragraphs.eachdo |paragraph| html << "<p>#{paragraph}</p>"end

• Use %w freely.

  STATES=%w(draftopenclosed)

• 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.

• 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#goodclassFooclass << selfattr_accessor:barendendFoo.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.

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!

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?