nathanpc/Ruby-StyleGuide.md

## Ruby-StyleGuide.md

      
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              Ruby-StyleGuide.md
            
          
    Ruby Style Guide

This style guide is based on the one used by GitHub, but with some changes that make the code a tiny bit more readable.


Use soft-tabs with a two space indent.


Keep each line of code to a readable length. Unless you have a reason to, keep lines to fewer than 100 characters.


Never leave trailing whitespace.


End each file with a newline.


Use spaces around operators, after commas, colons and semicolons, around {
and before }.


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

No spaces after !.

!array.include?(element)

Indent when as deep as case.

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
Classes


Avoid the usage of class (@@) variables due to their unusual 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.


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

Avoid class << self except when necessary, e.g. single accessors and aliased
attributes.

class TestClass
  # bad
  class << self
    def first_method
      # body omitted
    end

    def second_method_etc
      # body omitted
    end
  end

  # good
  class << self
    attr_accessor :per_page
    alias_method :nwo, :find_by_name_with_owner
  end

  def self.first_method
    # body omitted
  end

  def self.second_method_etc
    # body omitted
  end
end

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

class SomeClass
  def public_method
    # ...
  end

  private
  def private_method
    # ...
  end
end

Avoid explicit use of self as the recipient of internal class or instance
messages unless to specify a method shadowed by a variable.

class SomeClass
  attr_accessor :message

  def greeting(name)
    message = "Hi #{name}" # local variable in Ruby, not attribute writer
    self.message = message
  end
end
Collections


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)


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 }
Documentation

Use RDoc instead. Deprecated: Use TomDoc to the best of your ability. It's pretty sweet:
# Public: Duplicate some text an arbitrary number of times.
#
# text  - The String to be duplicated.
# count - The Integer number of times to duplicate the text.
#
# Examples
#
#   multiplex("Tom", 4)
#   # => "TomTomTomTom"
#
# Returns the duplicated String.
def multiplex(text, count)
  text * count
end
Dynamic Dispatch

Avoid calling send and its cousins unless you really need it. Metaprogramming can be extremely powerful, but in most cases you can write code that captures your meaning by being explicit:
# avoid 
unless [:base, :head].include?(base_or_head)
  raise ArgumentError, "base_or_head must be either :base or :head"
end

repository = pull.send("#{base_or_head}_repository")
branch = pull.send("#{base_or_head}_ref_name")

# prefer
case base_or_head
when :base
  repository = pull.base_repository
  branch = pull.base_ref_name
when :head
  repository = pull.head_repository
  branch = pull.head_ref_name
else
  raise ArgumentError, "base_or_head must be either :base or :head"
end
Exceptions


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

Rescue specific exceptions, not StandardError or its superclasses.

# bad
begin
  # an exception occurs here
rescue
  # exception handling
end

# still bad
begin
  # an exception occurs here
rescue Exception
  # exception handling
end
Hashes

Use the Ruby 1.9 syntax for hash literals when all the keys are symbols:
# good
user = {
  login: "defunkt",
  name: "Chris Wanstrath"
}

# bad
user = {
  :login => "defunkt",
  :name => "Chris Wanstrath"
}
Use the 1.9 syntax when calling a method with Hash options arguments or named arguments:
# good
user = User.create(login: "jane")
link_to("Account", controller: "users", action: "show", id: user)

# bad
user = User.create(:login => "jane")
link_to("Account", :controller => "users", :action => "show", :id => user)
If you have a hash with mixed key types, use the legacy hashrocket style to avoid mixing styles within the same hash:
# good
hsh = {
  :user_id => 55,
  "followers-count" => 1000
}

# bad
hsh = {
  user_id: 55,
  "followers-count" => 1000
}
Keyword Arguments

Keyword arguments are recommended but not required when a method's arguments may otherwise be opaque or non-obvious when called. Additionally, prefer them over the old "Hash as pseudo-named args" style from pre-2.0 ruby.
So instead of this:
def remove_member(user, skip_membership_check=false)
  # ...
end

# Elsewhere: what does true mean here?
remove_member(user, true)
Do this, which is much clearer.
def remove_member(user, skip_membership_check: false)
  # ...
end

# Elsewhere, now with more clarity:
remove_member user, skip_membership_check: true
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!, etc.) should end with an exclamation mark. Bang methods
should only exist if a non-bang method exists. (More on this).


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/(.*)$)
Regular Expressions


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

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.

string = "some injection\nusername"
string[/^username$/]   # matches
string[/\Ausername\z/] # don't match

Optional: 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
Requires

Always require dependencies used directly in a script at the start of the same file.
Resources that will get autoloaded on first use—such as Rails models, controllers, or
helpers—don't need to be required.
require 'set'
require 'time'

%w(foo bar).to_set
Time.parse("2015-10-21")
This not only loads the necessary dependencies if they haven't already, but acts as
documentation about the libraries that the current file uses.
Strings


Prefer string interpolation instead of string concatenation:

# bad
email_with_name = user.name + " <" + user.email + ">"

# good
email_with_name = "#{user.name} <#{user.email}>"

Use double-quoted strings. Interpolation and escaped characters
will always work without a delimiter change, and ' is a lot more
common than " in string literals.

# 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
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

Avoid the ternary operator (?:) except in cases where all expressions are extremely
trivial. However, do use the ternary operator(?:) over if/then/else/end constructs
for single line conditionals.

# 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


Avoid multi-line ?: (the ternary operator), use if/unless instead.


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


# bad
do_something if some_condition


# good
if some_condition
  do_something
end

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

Prefer do...end over {...} 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"]

# good
names.each do |name|
  puts name
end

# bad
names.each { |name| puts name }

# good
names.select { |name| name.start_with?("S") }.map { |name| name.upcase }

# bad
names.select do |name|
  name.start_with?("S")
end.map { |name| name.upcase }

Always use return.

# bad
def some_method(some_arr)
  some_arr.size
end


# good
def some_method(some_arr)
  return some_arr.size
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).

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

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

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

# also good - has correct precedence.
if (v = 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?


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. Prefer long form versions such as
$PROGRAM_NAME.


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).


Use _ for unused block parameters.


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

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


Don't use the === (threequals) operator to check types. === is mostly an
implementation detail to support Ruby features like case, and it's not commutative.
For example, String === "hi" is true and "hi" === String is false.
Instead, use is_a? or kind_of? if you must.
Refactoring is even better. It's worth looking hard at any code that explicitly checks types.