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 in 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 }.

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
```

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 an empty line before the return value of a method (unless it only has one line), and an 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. Don't put an empty line between the comment block and the def.
Use empty lines to break up a method into logical paragraphs.
Keep lines fewer than 80 characters. (Emacs users should really have a look at whitespace-mode.)
Avoid trailing whitespace. (Emacs users: Whitespace-mode again comes to the rescue.)

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.

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 x.odd? then
  puts "odd"
end

# good
if x.odd?
  puts "odd"
end

Favor if/then/else over the ternary operator. if is an expression in Ruby and the resulting code is arguably easier to read (albeit not as concise). Remember that "Programs must be written for people to read, and only incidentally for machines to execute." (Abelson and Sussman)
```
# good
result = if some_condition then something else something_else end

# not so good
result = some_condition ? something : something_else
```
Use when x; ... for one-line cases.
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 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. Another good alternative is the usage of control flow and/or.

# 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 global variables (like $0-9, $`, ...).

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 length of an identifier determines its scope. Use one-letter variables for short block/method parameters, according to this scheme:

  a,b,c: any object
  d: directory names
  e: elements of an Enumerable
  ex: rescued exceptions
  f: files and file names
  i,j: indexes
  k: the key part of a hash entry
  m: methods
  o: any object
  r: return values of short methods
  s: strings
  v: any value
  v: the value part of a hash entry
  x,y,z: numbers

And in general, the first letter of the class name if all objects are of that type.

When using inject with short blocks, name the arguments |a, e| (accumulator, element).
When defining binary operators, name the argument other.
```
def +(other)
  # body omitted
end
```
Prefer map over collect, find over detect, find_all over select, size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it.

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)
Comments longer than a word are capitalized and use punctuation. Use two spaces after periods.

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 in inheritance.
Assign methods proper visibility levels (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.

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
end

Add "global" methods to Kernel (if you have to) and make them private.
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 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

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!

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Abstract

Formatting

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Exceptions

Misc

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Contributing

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Abstract

Formatting

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Naming

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Classes

Exceptions

Misc

Design

Contributing