Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/uohzxela/clean-code-ruby

🛁 Clean Code concepts adapted for Ruby
https://github.com/uohzxela/clean-code-ruby

best-practices clean-code ruby

Last synced: 4 days ago
JSON representation

🛁 Clean Code concepts adapted for Ruby

Awesome Lists containing this project

README 

        
# clean-code-ruby



Clean Code concepts adapted for Ruby.



Inspired by [clean-code-javascript](https://github.com/ryanmcdermott/clean-code-javascript).



*Note: The examples are largely ported over from JavaScript so they may not be idiomatic. Feel free to point out any non-idiomatic Ruby code by submitting an issue and I'll correct it right away. Also, pull requests are always welcome!*



## Table of Contents

  1. [Introduction](#introduction)

  2. [Variables](#variables)

  3. [Methods](#methods)

  4. [Objects and Data Structures](#objects-and-data-structures)

  5. [Classes](#classes)

  6. [SOLID](#solid)

  7. [Testing](#testing)

  9. [Error Handling](#error-handling)

  10. [Formatting](#formatting)

  11. [Comments](#comments)

  12. [Translations](#translations)



## Introduction

![Humorous image of software quality estimation as a count of how many expletives

you shout when reading code](http://www.osnews.com/images/comics/wtfm.jpg)



Software engineering principles, from Robert C. Martin's book

[*Clean Code*](https://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882),

adapted for Ruby. This is not a style guide. It's a guide to producing

[readable, reusable, and refactorable](https://github.com/ryanmcdermott/3rs-of-software-architecture) software in Ruby.



Not every principle herein has to be strictly followed, and even fewer will be

universally agreed upon. These are guidelines and nothing more, but they are

ones codified over many years of collective experience by the authors of

*Clean Code*.



Our craft of software engineering is just a bit over 50 years old, and we are

still learning a lot. When software architecture is as old as architecture

itself, maybe then we will have harder rules to follow. For now, let these

guidelines serve as a touchstone by which to assess the quality of the

Ruby code that you and your team produce.



One more thing: knowing these won't immediately make you a better software

developer, and working with them for many years doesn't mean you won't make

mistakes. Every piece of code starts as a first draft, like wet clay getting

shaped into its final form. Finally, we chisel away the imperfections when

we review it with our peers. Don't beat yourself up for first drafts that need

improvement. Beat up the code instead!



## **Variables**

### Use meaningful and pronounceable variable names



**Bad:**

```ruby

yyyymmdstr = Time.now.strftime('%Y/%m/%d')

```



**Good:**

```ruby

current_date = Time.now.strftime('%Y/%m/%d')

```

**[⬆ back to top](#table-of-contents)**



### Use the same vocabulary for the same type of variable



Pick one word for the concept and stick to it.



**Bad:**

```ruby

user_info

user_data

user_record



starts_at

start_at

start_time

```



**Good:**

```ruby

user



starts_at

```

**[⬆ back to top](#table-of-contents)**



### Use searchable names and use constants

We will read more code than we will ever write. It's important that the code we

do write is readable and searchable. By *not* naming variables that end up

being meaningful for understanding our program, we hurt our readers.

Make your names searchable.



Also, instead of hardcoding values and using "magic numbers", create constants.



**Bad:**

```ruby

# What the heck is 86400 for?

status = Timeout::timeout(86_400) do

  # ...

end

```



**Good:**

```ruby

# Declare them as capitalized globals.

SECONDS_IN_A_DAY = 86_400



status = Timeout::timeout(SECONDS_IN_A_DAY) do

  # ...

end

```

**[⬆ back to top](#table-of-contents)**



### Use explanatory variables

**Bad:**

```ruby

address = 'One Infinite Loop, Cupertino 95014'

city_zip_code_regex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/

save_city_zip_code(city_zip_code_regex.match(address)[1], city_zip_code_regex.match(address)[2])

```



**Good:**

```ruby

address = 'One Infinite Loop, Cupertino 95014'

city_zip_code_regex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/

_, city, zip_code = city_zip_code_regex.match(address).to_a

save_city_zip_code(city, zip_code)

```

**[⬆ back to top](#table-of-contents)**



### Avoid Mental Mapping

Explicit is better than implicit.



**Bad:**

```ruby

locations = ['Austin', 'New York', 'San Francisco']

locations.each do |l|

  do_stuff

  do_some_other_stuff

  # ...

  # ...

  # ...

  # Wait, what is `l` for again?

  dispatch(l)

end

```



**Good:**

```ruby

locations = ['Austin', 'New York', 'San Francisco']

locations.each do |location|

  do_stuff

  do_some_other_stuff

  # ...

  # ...

  # ...

  dispatch(location)

end

```

**[⬆ back to top](#table-of-contents)**



### Don't add unneeded context

If your class/object name tells you something, don't repeat that in your

variable name.



**Bad:**

```ruby

car = {

  car_make: 'Honda',

  car_model: 'Accord',

  car_color: 'Blue'

}



def paint_car(car)

  car[:car_color] = 'Red'

end

```



**Good:**

```ruby

car = {

  make: 'Honda',

  model: 'Accord',

  color: 'Blue'

}



def paint_car(car)

  car[:color] = 'Red'

end

```

**[⬆ back to top](#table-of-contents)**



### Use default arguments instead of short circuiting or conditionals

Default arguments are often cleaner than short circuiting. Be aware that if you use them, your method will only provide default values for undefined arguments. Other "falsy" values such as `false` and `nil` will not be replaced by a default value.



**Bad:**

```ruby

def create_micro_brewery(name)

  brewery_name = name || 'Hipster Brew Co.'

  # ...

end

```



**Good:**

```ruby

def create_micro_brewery(brewery_name = 'Hipster Brew Co.')

  # ...

end

```

**[⬆ back to top](#table-of-contents)**



## **Methods**

### Method arguments (2 or fewer ideally)

Limiting the amount of method parameters is incredibly important because it

makes testing your method easier. Having more than three leads to a

combinatorial explosion where you have to test tons of different cases with

each separate argument.



One or two arguments is the ideal case, and three should be avoided if possible.

Anything more than that should be consolidated. Usually, if you have

more than two arguments then your method is trying to do too much. In cases

where it's not, most of the time a higher-level object will suffice as an

argument. Or you can pass data to the method by instance variables.



Since Ruby allows you to make objects on the fly, without a lot of class

boilerplate, you can use an object if you are finding yourself needing a

lot of arguments. The prevailing pattern in Ruby is to use a hash of arguments.



To make it obvious what properties the method expects, you can use the keyword arguments syntax (introduced in Ruby 2.1). This has a few advantages:



1. When someone looks at the method signature, it's immediately clear what

properties are being used.

2. If a required keyword argument is missing, Ruby will raise a useful `ArgumentError` that tells us which required argument we must include.



**Bad:**

```ruby

def create_menu(title, body)

  # ...

end



create_menu('Foo', 'Bar')

```



**Good:**

```ruby

def create_menu(title:, body:)

  # ...

end



create_menu(title: 'Foo', body: 'Bar')

```

**[⬆ back to top](#table-of-contents)**



### Methods should do one thing

This is by far the most important rule in software engineering. When methods

do more than one thing, they are harder to compose, test, and reason about.

When you can isolate a method to just one action, they can be refactored

easily and your code will read much cleaner. If you take nothing else away from

this guide other than this, you'll be ahead of many developers.



**Bad:**

```ruby

def email_clients(clients)

  clients.each do |client|

    client_record = database.lookup(client)

    email(client) if client_record.active?

  end

end



email_clients(clients)

```



**Good:**

```ruby

def email_clients(clients)

  clients.each { |client| email(client) }

end



def active(objects)

  objects.select { |object| active?(object) }

end



def active?(object)

  record = database.lookup(object)

  record.active?

end



email_clients(active(clients))

```

**[⬆ back to top](#table-of-contents)**



### Method names should say what they do

Poorly named methods add to the code reviewer's cognitive load at best, and mislead the

code reviewer at worst. Strive to capture the precise intent when naming methods.



**Bad:**

```ruby

def add_to_date(date, month)

  # ...

end



date = DateTime.now



# It's hard to tell from the method name what is added

add_to_date(date, 1)

```



**Good:**

```ruby

def add_month_to_date(date, month)

  # ...

end



date = DateTime.now

add_month_to_date(date, 1)

```

**[⬆ back to top](#table-of-contents)**



### Methods should only be one level of abstraction

When you have more than one level of abstraction your method is usually

doing too much. Splitting up methods leads to reusability and easier

testing. Furthermore, methods should descend by the level of abstraction: one very abstract method should call methods that are less abstract and so on.



**Bad:**

```ruby

def interpret(code)

  regexes = [

    # ...

  ]

  statements = code.split(' ')



  tokens = regexes.each_with_object([]) do |regex, memo|

    statements.each do |statement|

      # memo.push(...)

    end

  end



  ast = tokens.map do |token|

    # ...

  end



  ast.map do |node|

    # ...

  end

end

```



**Good:**

```ruby

def interpret(code)

  tokens = tokenize(code)

  ast = lex(tokens)

  parse(ast)

end



def tokenize(code)

  regexes = [

    # ...

  ]

  statements = code.split(' ')



  regexes.each_with_object([]) do |regex, tokens|

    statements.each do |statement|

      # tokens.push(...)

    end

  end

end



def lex(tokens)

  tokens.map do |token|

    # ...

  end

end



def parse(ast)

  ast.map do |node|

    # ...

  end

end

```

**[⬆ back to top](#table-of-contents)**



### Remove duplicate code

Do your absolute best to avoid duplicate code. Duplicate code is bad because it

means that there's more than one place to alter something if you need to change

some logic.



Imagine if you run a restaurant and you keep track of your inventory: all your

tomatoes, onions, garlic, spices, etc. If you have multiple lists that

you keep this on, then all have to be updated when you serve a dish with

tomatoes in them. If you only have one list, there's only one place to update!



Oftentimes you have duplicate code because you have two or more slightly

different things, that share a lot in common, but their differences force you

to have two or more separate methods that do much of the same things. Removing

duplicate code means creating an abstraction that can handle this set of

different things with just one method/module/class.



Getting the abstraction right is critical, that's why you should follow the

SOLID principles laid out in the *Classes* section. Bad abstractions can be

worse than duplicate code, so be careful! Having said this, if you can make

a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself

updating multiple places anytime you want to change one thing.



**Bad:**

```ruby

def show_developer_list(developers)

  developers.each do |developer|

    data = {

      expected_salary: developer.expected_salary,

      experience: developer.experience,

      github_link: developer.github_link

    }



    render(data)

  end

end



def show_manager_list(managers)

  managers.each do |manager|

    data = {

      expected_salary: manager.expected_salary,

      experience: manager.experience,

      portfolio: manager.mba_projects

    }



    render(data)

  end

end

```



**Good:**

```ruby

def show_employee_list(employees)

  employees.each do |employee|

    data = build_data(employee)

    render(data)

  end

end



def build_data(employee)

  general_data = {

    expected_salary: employee.expected_salary,

    experience: employee.experience

  }



  general_data.merge(position_specific_data(employee))

end



def position_specific_data(employee)

  case employee.type

  when 'manager'

    { portfolio: employee.mba_projects }

  when 'developer'

    { github_link: employee.github_link }

  end

end

```

**[⬆ back to top](#table-of-contents)**



### Don't use flags as method parameters

Flags tell your user that this method does more than one thing. Methods should do one thing. Split out your methods if they are following different code paths based on a boolean.



**Bad:**

```ruby

def create_file(name, temp)

  if temp

    fs.create("./temp/#{name}")

  else

    fs.create(name)

  end

end

```



**Good:**

```ruby

def create_file(name)

  fs.create(name)

end



def create_temp_file(name)

  create_file("./temp/#{name}")

end

```

**[⬆ back to top](#table-of-contents)**



### Avoid Side Effects (part 1)

A method produces side effects if it does anything more than take values and/or

return values. A side effect could be writing to a file,

modifying some global variable, or accidentally wiring all your money to a

stranger.



Now, you do need to have side effects in a program on occasion. Like the previous

example, you might need to write to a file. What you want to do is to

centralize where you are doing this. Don't have several methods and classes

that write to a particular file. Have one service that does it. One and only one.



The main point is to avoid common pitfalls like sharing state between objects

without any structure, using mutable data types that can be written to by anything,

and not centralizing where your side effects occur. If you can do this, you will

be happier than the vast majority of other programmers.



**Bad:**

```ruby

# Global variable referenced by following method.

# If we had another method that used this name, now it'd be an array and it could break it.

$name = 'Ryan McDermott'



def split_into_first_and_last_name

  $name = $name.split(' ')

end



split_into_first_and_last_name()



puts $name # ['Ryan', 'McDermott']

```



**Good:**

```ruby

def split_into_first_and_last_name(name)

  name.split(' ')

end



name = 'Ryan McDermott'

first_and_last_name = split_into_first_and_last_name(name)



puts name # 'Ryan McDermott'

puts first_and_last_name # ['Ryan', 'McDermott']

```

**[⬆ back to top](#table-of-contents)**



### Avoid Side Effects (part 2)

In Ruby, everything is an object and everything is passed by value, but these values are references to objects. In the case of objects and arrays, if your method makes a change

in a shopping cart array, for example, by adding an item to purchase,

then any other method that uses that `cart` array will be affected by this

addition. That may be great, however it can be bad too. Let's imagine a bad

situation:



The user clicks the "Purchase", button which calls a `purchase` method that

spawns a network request and sends the `cart` array to the server. Because

of a bad network connection, the `purchase` method has to keep retrying the

request. Now, what if in the meantime the user accidentally clicks "Add to Cart"

button on an item they don't actually want before the network request begins?

If that happens and the network request begins, then that purchase method

will send the accidentally added item because it has a reference to a shopping

cart array that the `add_item_to_cart` method modified by adding an unwanted

item.



A great solution would be for the `add_item_to_cart` to always clone the `cart`,

edit it, and return the clone. This ensures that no other methods that are

holding onto a reference of the shopping cart will be affected by any changes.



Two caveats to mention to this approach:

  1. There might be cases where you actually want to modify the input object,

but when you adopt this programming practice you will find that those cases

are pretty rare. Most things can be refactored to have no side effects!



  2. Cloning big objects can be very expensive in terms of performance. Luckily,

this isn't a big issue in practice because there are

[great gems](https://github.com/hamstergem/hamster) that allow

this kind of programming approach to be fast and not as memory intensive as

it would be for you to manually clone objects and arrays.



**Bad:**

```ruby

def add_item_to_cart(cart, item)

  cart.push(item: item, time: Time.now)

end

```



**Good:**

```ruby

def add_item_to_cart(cart, item)

  cart + [{ item: item, time: Time.now }]

end

```

**[⬆ back to top](#table-of-contents)**



### Favor functional programming over imperative programming

Ruby isn't a functional language in the way that Haskell is, but it has

a functional flavor to it. Functional languages are cleaner and easier to test.

Favor this style of programming when you can.



**Bad:**

```ruby

programmer_output = [

  {

    name: 'Uncle Bobby',

    lines_of_code: 500

  }, {

    name: 'Suzie Q',

    lines_of_code: 1500

  }, {

    name: 'Jimmy Gosling',

    lines_of_code: 150

  }, {

    name: 'Grace Hopper',

    lines_of_code: 1000

  }

]



total_output = 0



programmer_output.each do |output|

  total_output += output[:lines_of_code]

end

```



**Good:**

```ruby

programmer_output = [

  {

    name: 'Uncle Bobby',

    lines_of_code: 500

  }, {

    name: 'Suzie Q',

    lines_of_code: 1500

  }, {

    name: 'Jimmy Gosling',

    lines_of_code: 150

  }, {

    name: 'Grace Hopper',

    lines_of_code: 1000

  }

]



INITIAL_VALUE = 0



total_output = programmer_output.sum(INITIAL_VALUE) { |output| output[:lines_of_code] }

```

**[⬆ back to top](#table-of-contents)**



### Encapsulate conditionals



**Bad:**

```ruby

if params[:message].present? && params[:recipient].present?

  # ...

end

```



**Good:**

```ruby

def send_message?(params)

  params[:message].present? && params[:recipient].present?

end



if send_message?(params)

  # ...

end

```

**[⬆ back to top](#table-of-contents)**



### Avoid negative conditionals



**Bad:**

```ruby

if !genres.blank?

  # ...

end

```



**Good:**

```ruby

unless genres.blank?

  # ...

end



# or



if genres.present?

  # ...

end

```

**[⬆ back to top](#table-of-contents)**



### Avoid conditionals

This seems like an impossible task. Upon first hearing this, most people say,

"how am I supposed to do anything without an `if` statement?" The answer is that

you can use polymorphism to achieve the same task in many cases. The second

question is usually, "well that's great but why would I want to do that?" The

answer is a previous clean code concept we learned: a method should only do

one thing. When you have classes and methods that have `if` statements, you

are telling your user that your method does more than one thing. Remember,

just do one thing.



**Bad:**

```ruby

class Airplane

  # ...

  def cruising_altitude

    case @type

    when '777'

      max_altitude - passenger_count

    when 'Air Force One'

      max_altitude

    when 'Cessna'

      max_altitude - fuel_expenditure

    end

  end

end

```



**Good:**

```ruby

class Airplane

  # ...

end



class Boeing777 < Airplane

  # ...

  def cruising_altitude

    max_altitude - passenger_count

  end

end



class AirForceOne < Airplane

  # ...

  def cruising_altitude

    max_altitude

  end

end



class Cessna < Airplane

  # ...

  def cruising_altitude

    max_altitude - fuel_expenditure

  end

end

```

**[⬆ back to top](#table-of-contents)**



### Avoid type-checking (part 1)

Ruby is dynamically typed, which means your methods can take any type of argument.

Sometimes you are bitten by this freedom and it becomes tempting to do

type-checking in your methods. There are many ways to avoid having to do this.

The first thing to consider is consistent APIs.



**Bad:**

```ruby

def travel_to_texas(vehicle)

  if vehicle.is_a?(Bicycle)

    vehicle.pedal(@current_location, Location.new('texas'))

  elsif vehicle.is_a?(Car)

    vehicle.drive(@current_location, Location.new('texas'))

  end

end

```



**Good:**

```ruby

def travel_to_texas(vehicle)

  vehicle.move(@current_location, Location.new('texas'))

end

```

**[⬆ back to top](#table-of-contents)**



### Avoid type-checking (part 2)

If you are working with basic values like strings and integers,

and you can't use polymorphism but you still feel the need to type-check,

you should consider using [contracts.ruby](https://github.com/egonSchiele/contracts.ruby). The problem with manually type-checking Ruby is that

doing it well requires so much extra verbiage that the faux "type-safety" you get

doesn't make up for the lost readability. Keep your Ruby clean, write

good tests, and have good code reviews.



**Bad:**

```ruby

def combine(val1, val2)

  if (val1.is_a?(Numeric) && val2.is_a?(Numeric)) ||

     (val1.is_a?(String) && val2.is_a?(String))

    return val1 + val2

  end



  raise 'Must be of type String or Numeric'

end

```



**Good:**

```ruby

def combine(val1, val2)

  val1 + val2

end

```

**[⬆ back to top](#table-of-contents)**



### Remove dead code

Dead code is just as bad as duplicate code. There's no reason to keep it in

your codebase. If it's not being called, get rid of it! It will still be safe

in your version history if you still need it.



**Bad:**

```ruby

def old_request_module(url)

  # ...

end



def new_request_module(url)

  # ...

end



req = new_request_module(request_url)

inventory_tracker('apples', req, 'www.inventory-awesome.io')

```



**Good:**

```ruby

def new_request_module(url)

  # ...

end



req = new_request_module(request_url)

inventory_tracker('apples', req, 'www.inventory-awesome.io')

```

**[⬆ back to top](#table-of-contents)**



## **Objects and Data Structures**

### Use getters and setters

Using getters and setters to access data on objects could be better than simply

looking for a property on an object. "Why?" you might ask. Well, here's an

unorganized list of reasons why:



* When you want to do more beyond getting an object property, you don't have

to look up and change every accessor in your codebase.

* Makes adding validation simple when doing a `set`.

* Encapsulates the internal representation.

* Easy to add logging and error handling when getting and setting.

* You can lazy load your object's properties, let's say getting it from a

server.



**Bad:**

```ruby

def make_bank_account

  # ...



  {

    balance: 0

    # ...

  }

end



account = make_bank_account

account[:balance] = 100

account[:balance] # => 100

```



**Good:**

```ruby

class BankAccount

  def initialize

    # this one is private

    @balance = 0

  end



  # a "getter" via a public instance method

  def balance

    # do some logging

    @balance

  end



  # a "setter" via a public instance method

  def balance=(amount)

    # do some logging

    # do some validation

    @balance = amount

  end

end



account = BankAccount.new

account.balance = 100

account.balance # => 100

```



Alternatively, if your getters and setters are absolutely trivial, you should use `attr_accessor` to define them. This is especially convenient for implementing data-like objects which expose data to other parts of the system (e.g., ActiveRecord objects, response wrappers for remote APIs).



**Good:**

```ruby

class Toy

  attr_accessor :price

end



toy = Toy.new

toy.price = 50

toy.price # => 50

```



However, you have to be aware that in some situations, using `attr_accessor` is a code smell, read more [here](https://solnic.codes/2012/04/04/get-rid-of-that-code-smell-attributes).



**[⬆ back to top](#table-of-contents)**



## **Classes**



### Avoid fluent interfaces

A [Fluent interface](https://en.wikipedia.org/wiki/Fluent_interface) is an object

oriented API that aims to improve the readability of the source code by using

[method chaining](https://en.wikipedia.org/wiki/Method_chaining).



While there can be some contexts, frequently builder objects, where this

pattern reduces the verbosity of the code (e.g., ActiveRecord queries),

more often it comes at some costs:



1. Breaks [Encapsulation](https://en.wikipedia.org/wiki/Encapsulation_%28object-oriented_programming%29)

2. Breaks [Decorators](https://en.wikipedia.org/wiki/Decorator_pattern)

3. Is harder to [mock](https://en.wikipedia.org/wiki/Mock_object) in a test suite

4. Makes diffs of commits harder to read



For more information you can read the full [blog post](https://ocramius.github.io/blog/fluent-interfaces-are-evil/)

on this topic written by [Marco Pivetta](https://github.com/Ocramius).



**Bad:**

```ruby

class Car

  def initialize(make, model, color)

    @make = make

    @model = model

    @color = color

    # NOTE: Returning self for chaining

    self

  end



  def set_make(make)

    @make = make

    # NOTE: Returning self for chaining

    self

  end



  def set_model(model)

    @model = model

    # NOTE: Returning self for chaining

    self

  end



  def set_color(color)

    @color = color

    # NOTE: Returning self for chaining

    self

  end



  def save

    # save object...

    # NOTE: Returning self for chaining

    self

  end

end



car = Car.new('Ford','F-150','red')

  .set_color('pink')

  .save

```



**Good:**

```ruby

class Car

  attr_accessor :make, :model, :color



  def initialize(make, model, color)

    @make = make

    @model = model

    @color = color

  end



  def save

    # Save object...

  end

end



car = Car.new('Ford', 'F-150', 'red')

car.color = 'pink'

car.save

```

**[⬆ back to top](#table-of-contents)**



### Prefer composition over inheritance

As stated famously in [*Design Patterns*](https://en.wikipedia.org/wiki/Design_Patterns) by the Gang of Four,

you should prefer composition over inheritance where you can. There are lots of

good reasons to use inheritance and lots of good reasons to use composition.

The main point for this maxim is that if your mind instinctively goes for

inheritance, try to think if composition could model your problem better. In some

cases, it can.



You might be wondering then, "when should I use inheritance?" It

depends on your problem at hand, but this is a decent list of when inheritance

makes more sense than composition:



1. Your inheritance represents an "is-a" relationship and not a "has-a"

relationship (Human->Animal vs. User->UserDetails).

2. You can reuse code from the base classes (Humans can move like all animals).

3. You want to make global changes to derived classes by changing a base class.

(Change the caloric expenditure of all animals when they move).



**Bad:**

```ruby

class Employee

  def initialize(name, email)

    @name = name

    @email = email

  end



  # ...

end



# Bad because Employees "have" tax data. EmployeeTaxData is not a type of Employee

class EmployeeTaxData < Employee

  def initialize(ssn, salary)

    @ssn = ssn

    @salary = salary

  end



  # ...

end

```



**Good:**

```ruby

class EmployeeTaxData

  def initialize(ssn, salary)

    @ssn = ssn

    @salary = salary

  end



  # ...

end



class Employee

  def initialize(name, email)

    @name = name

    @email = email

  end



  def set_tax_data(ssn, salary)

    @tax_data = EmployeeTaxData.new(ssn, salary)

  end

  # ...

end

```

**[⬆ back to top](#table-of-contents)**



## **SOLID**

### Single Responsibility Principle (SRP)

As stated in Clean Code, "There should never be more than one reason for a class

to change". It's tempting to jam-pack a class with a lot of functionality, like

when you can only take one suitcase on your flight. The issue with this is

that your class won't be conceptually cohesive and it will give it many reasons

to change. Minimizing the number of times you need to change a class is important.

It's important because if too much functionality is in one class and you modify

a piece of it, it can be difficult to understand how that will affect other

dependent modules in your codebase.



**Bad:**

```ruby

class UserSettings

  def initialize(user)

    @user = user

  end



  def change_settings(settings)

    return unless valid_credentials?

    # ...

  end



  def valid_credentials?

    # ...

  end

end

```



**Good:**

```ruby

class UserAuth

  def initialize(user)

    @user = user

  end



  def valid_credentials?

    # ...

  end

end



class UserSettings

  def initialize(user)

    @user = user

    @auth = UserAuth.new(user)

  end



  def change_settings(settings)

    return unless @auth.valid_credentials?

    # ...

  end

end

```

**[⬆ back to top](#table-of-contents)**



### Open/Closed Principle (OCP)

As stated by [Bertrand Meyer](https://en.wikipedia.org/wiki/Bertrand_Meyer), "software entities (classes, modules, functions,

etc.) should be open for extension, but closed for modification." What does that

mean though? This principle basically states that you should allow users to

add new functionalities without changing existing code.



In the "bad" example below adding another adapter would require changing `HttpRequester` class. This violates OCP.



**Bad:**

```ruby

class AjaxAdapter

  attr_reader :name



  def initialize

    @name = 'ajaxAdapter'

  end

end



class NodeAdapter

  attr_reader :name



  def initialize

    @name = 'nodeAdapter'

  end

end



class HttpRequester

  def initialize(adapter)

    @adapter = adapter

  end



  def fetch(url)

    case @adapter.name

    when 'ajaxAdapter'

      make_ajax_call(url)

    when 'nodeAdapter'

      make_http_call(url)

    end

  end



  def make_ajax_call(url)

    # ...

  end



  def make_http_call(url)

    # ...

  end

end

```



**Good:**

```ruby

class AjaxAdapter

  def request(url)

    # ...

  end

end



class NodeAdapter

  def request(url)

    # ...

  end

end



class HttpRequester

  def initialize(adapter)

    @adapter = adapter

  end



  def fetch(url)

    @adapter.request(url)

  end

end

```

**[⬆ back to top](#table-of-contents)**



### Liskov Substitution Principle (LSP)

This is a scary term for a very simple concept. It's formally defined as "If S

is a subtype of T, then objects of type T may be replaced with objects of type S

(i.e., objects of type S may substitute objects of type T) without altering any

of the desirable properties of that program (correctness, task performed,

etc.)." That's an even scarier definition.



The best explanation for this is if you have a parent class and a child class,

then the base class can always be replaced by the child class without getting

incorrect results. This might still be confusing, so let's take a look at the

classic Square-Rectangle example. Mathematically, a square is a rectangle, but

if you model it using the "is-a" relationship via inheritance, you quickly

get into trouble.



**Bad:**

```ruby

class Rectangle

  def initialize

    @width = 0

    @height = 0

  end



  def color=(color)

    # ...

  end



  def render(area)

    # ...

  end



  def width=(width)

    @width = width

  end



  def height=(height)

    @height = height

  end



  def area

    @width * @height

  end

end



class Square < Rectangle

  def width=(width)

    @width = width

    @height = width

  end



  def height=(height)

    @width = height

    @height = height

  end

end



def render_large_rectangles(rectangles)

  rectangles.each do |rectangle|

    rectangle.width = 4

    rectangle.height = 5

    area = rectangle.area # BAD: Returns 25 for Square. Should be 20.

    rectangle.render(area)

  end

end



rectangles = [Rectangle.new, Rectangle.new, Square.new]

render_large_rectangles(rectangles)

```



**Good:**

```ruby

class Shape

  def color=(color)

    # ...

  end



  def render(area)

    # ...

  end

end



class Rectangle < Shape

  def initialize(width, height)

    @width = width

    @height = height

  end



  def area

    @width * @height

  end

end



class Square < Shape

  def initialize(length)

    @length = length

  end



  def area

    @length * @length

  end

end



def render_large_shapes(shapes)

  shapes.each do |shape|

    area = shape.area

    shape.render(area)

  end

end



shapes = [Rectangle.new(4, 5), Rectangle.new(4, 5), Square.new(5)]

render_large_shapes(shapes)

```

**[⬆ back to top](#table-of-contents)**



### Interface Segregation Principle (ISP)

Ruby doesn't have interfaces so this principle doesn't apply as strictly

as others. However, it's important and relevant even with Ruby's lack of

type system.



ISP states that "Clients should not be forced to depend upon interfaces that

they do not use." Interfaces are implicit contracts in Ruby because of

duck typing.



When a client depends upon a class that contains interfaces that the client does not use, but that other clients do use, then that client will be affected by the changes that those other clients force upon the class.



The following example is taken from [here](http://geekhmer.github.io/blog/2015/03/18/interface-segregation-principle-in-ruby/).



**Bad:**

```ruby

class Car

  # used by Driver

  def open

    # ...

  end



  # used by Driver

  def start_engine

    # ...

  end



  # used by Mechanic

  def change_engine

    # ...

  end

end



class Driver

  def drive

    @car.open

    @car.start_engine

  end

end



class Mechanic

  def do_stuff

    @car.change_engine

  end

end



```



**Good:**

```ruby

# used by Driver only

class Car

  def open

    # ...

  end



  def start_engine

    # ...

  end

end



# used by Mechanic only

class CarInternals

  def change_engine

    # ...

  end

end



class Driver

  def drive

    @car.open

    @car.start_engine

  end

end



class Mechanic

  def do_stuff

    @car_internals.change_engine

  end

end

```



**[⬆ back to top](#table-of-contents)**



### Dependency Inversion Principle (DIP)

This principle states two essential things:

1. High-level modules should not depend on low-level modules. Both should

depend on abstractions.

2. Abstractions should not depend upon details. Details should depend on

abstractions.



Simply put, DIP keeps high-level

modules from knowing the details of its low-level modules and setting them up.

It can accomplish this through dependency injection. A huge benefit of this is that

it reduces the coupling between modules. Coupling is a very bad development pattern

because it makes your code hard to refactor.



As stated previously, Ruby doesn't have interfaces so the abstractions

that are depended upon are implicit contracts. That is to say, the methods

and properties that an object/class exposes to another object/class. In the

example below, the implicit contract is that any Request module for an

`InventoryTracker` will have a `request_items` method.



**Bad:**

```ruby

class InventoryRequester

  def initialize

    @req_methods = ['HTTP']

  end



  def request_item(item)

    # ...

  end

end



class InventoryTracker

  def initialize(items)

    @items = items



    # BAD: We have created a dependency on a specific request implementation.

    @requester = InventoryRequester.new

  end



  def request_items

    @items.each do |item|

      @requester.request_item(item)

    end

  end

end



inventory_tracker = InventoryTracker.new(['apples', 'bananas'])

inventory_tracker.request_items

```



**Good:**

```ruby

class InventoryTracker

  def initialize(items, requester)

    @items = items

    @requester = requester

  end



  def request_items

    @items.each do |item|

      @requester.request_item(item)

    end

  end

end



class InventoryRequesterV1

  def initialize

    @req_methods = ['HTTP']

  end



  def request_item(item)

    # ...

  end

end



class InventoryRequesterV2

  def initialize

    @req_methods = ['WS']

  end



  def request_item(item)

    # ...

  end

end



# By constructing our dependencies externally and injecting them, we can easily

# substitute our request module for a fancy new one that uses WebSockets.

inventory_tracker = InventoryTracker.new(['apples', 'bananas'], InventoryRequesterV2.new)

inventory_tracker.request_items

```

**[⬆ back to top](#table-of-contents)**



## **Testing**

Testing is more important than shipping. If you have no tests or an

inadequate amount, then every time you ship code you won't be sure that you

didn't break anything. Deciding on what constitutes an adequate amount is up

to your team, but having 100% coverage (all statements and branches) is how

you achieve very high confidence and developer peace of mind. This means that

in addition to having a [great testing framework](http://rspec.info/), you also need to use a

[good coverage tool](https://coveralls.io/).



There's no excuse to not write tests. Aim to always write tests

for every new feature/module you introduce. If your preferred method is

Test Driven Development (TDD), that is great, but the main point is to just

make sure you are reaching your coverage goals before launching any feature,

or refactoring an existing one.



### Single expectation per test



**Bad:**

```ruby

require 'rspec'



describe 'Calculator' do

  let(:calculator) { Calculator.new }



  it 'performs addition, subtraction, multiplication and division' do

    expect(calculator.calculate('1 + 2')).to eq(3)

    expect(calculator.calculate('4 - 2')).to eq(2)

    expect(calculator.calculate('2 * 3')).to eq(6)

    expect(calculator.calculate('6 / 2')).to eq(3)

  end

end

```



**Good:**

```ruby

require 'rspec'



describe 'Calculator' do

  let(:calculator) { Calculator.new }



  it 'performs addition' do

    expect(calculator.calculate('1 + 2')).to eq(3)

  end



  it 'performs subtraction' do

    expect(calculator.calculate('4 - 2')).to eq(2)

  end



  it 'performs multiplication' do

    expect(calculator.calculate('2 * 3')).to eq(6)

  end



  it 'performs division' do

    expect(calculator.calculate('6 / 2')).to eq(3)

  end

end

```

**[⬆ back to top](#table-of-contents)**



## **Error Handling**

Thrown errors are a good thing! They mean the runtime has successfully

identified when something in your program has gone wrong and it's letting

you know by stopping method execution on the current stack, killing the

process, and notifying you in the logs with a stack trace.



### Don't ignore caught errors

Doing nothing with a caught error doesn't give you the ability to ever fix

or react to said error. Logging the error

isn't much better as often times it can get lost in a sea of other logs. If you wrap any bit of code in a `begin/rescue` it means you

think an error may occur there and therefore you should have a plan,

or create a code path, for when it occurs.



**Bad:**

```ruby

require 'logger'



logger = Logger.new(STDOUT)



begin

  method_that_might_throw()

rescue StandardError => err

  logger.info(err)

end

```



**Good:**

```ruby

require 'logger'



logger = Logger.new(STDOUT)

# Change the logger level to ERROR to output only logs with ERROR level and above

logger.level = Logger::ERROR



begin

  method_that_might_throw()

rescue StandardError => err

  # Option 1: Only log errors

  logger.error(err)

  # Option 2: Notify end-user via an interface

  notify_user_of_error(err)

  # Option 3: Report error to a third-party service like Honeybadger

  report_error_to_service(err)

  # OR do all three!

end

```



### Provide context with exceptions

Use a descriptive error class name and a message when you raise an error. That way you know why the error occurred and you can rescue the specific type of error.



***Bad:***

```ruby

def initialize(user)

  fail unless user

  ...

end

```



***Good:***

```ruby

def initialize(user)

  fail ArgumentError, 'Missing user' unless user

  ...

end

```



**[⬆ back to top](#table-of-contents)**



## **Formatting**

Formatting is subjective. Like many rules herein, there is no hard and fast

rule that you must follow. The main point is DO NOT ARGUE over formatting.

There are tons of tools like [RuboCop](https://github.com/bbatsov/rubocop) to automate this.

Use one! It's a waste of time and money for engineers to argue over formatting.



For things that don't fall under the purview of automatic formatting

(indentation, tabs vs. spaces, double vs. single quotes, etc.) look here

for some guidance.



### Use consistent capitalization

Ruby is dynamically typed, so capitalization tells you a lot about your variables,

methods, etc. These rules are subjective, so your team can choose whatever

they want. The point is, no matter what you all choose, just be consistent.



**Bad:**

```ruby

DAYS_IN_WEEK = 7

daysInMonth = 30



songs = ['Back In Black', 'Stairway to Heaven', 'Hey Jude']

Artists = ['ACDC', 'Led Zeppelin', 'The Beatles']



def eraseDatabase; end



def restore_database; end



class ANIMAL; end

class Alpaca; end

```



**Good:**

```ruby

DAYS_IN_WEEK = 7

DAYS_IN_MONTH = 30



SONGS = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'].freeze

ARTISTS = ['ACDC', 'Led Zeppelin', 'The Beatles'].freeze



def erase_database; end



def restore_database; end



class Animal; end

class Alpaca; end

```

**[⬆ back to top](#table-of-contents)**



### Method callers and callees should be close

If a method calls another, keep those methods vertically close in the source

file. Ideally, keep the caller right above the callee. We tend to read code from

top-to-bottom, like a newspaper. Because of this, make your code read that way.



**Bad:**

```ruby

class PerformanceReview

  def initialize(employee)

    @employee = employee

  end



  def lookup_peers

    db.lookup(@employee, :peers)

  end



  def lookup_manager

    db.lookup(@employee, :manager)

  end



  def peer_reviews

    peers = lookup_peers

    # ...

  end



  def perf_review

    peer_reviews

    manager_review

    self_review

  end



  def manager_review

    manager = lookup_manager

    # ...

  end



  def self_review

    # ...

  end

end



review = PerformanceReview.new(employee)

review.perf_review

```



**Good:**

```ruby

class PerformanceReview

  def initialize(employee)

    @employee = employee

  end



  def perf_review

    peer_reviews

    manager_review

    self_review

  end



  def peer_reviews

    peers = lookup_peers

    # ...

  end



  def lookup_peers

    db.lookup(@employee, :peers)

  end



  def manager_review

    manager = lookup_manager

    # ...

  end



  def lookup_manager

    db.lookup(@employee, :manager)

  end



  def self_review

    # ...

  end

end



review = PerformanceReview.new(employee)

review.perf_review

```



**[⬆ back to top](#table-of-contents)**



## **Comments**



### Don't leave commented out code in your codebase

Version control exists for a reason. Leave old code in your history.



**Bad:**

```ruby

do_stuff

# do_other_stuff

# do_some_more_stuff

# do_so_much_stuff

```



**Good:**

```ruby

do_stuff

```

**[⬆ back to top](#table-of-contents)**



### Don't have journal comments

Remember, use version control! There's no need for dead code, commented code,

and especially journal comments. Use `git log` to get history!



**Bad:**

```ruby

# 2016-12-20: Removed monads, didn't understand them (RM)

# 2016-10-01: Improved using special monads (JP)

# 2016-02-03: Removed type-checking (LI)

# 2015-03-14: Added combine with type-checking (JR)

def combine(a, b)

  a + b

end

```



**Good:**

```ruby

def combine(a, b)

  a + b

end

```

**[⬆ back to top](#table-of-contents)**



## Translations



This is also available in other languages:



  - [Brazilian Portuguese](https://github.com/uohzxela/clean-code-ruby/blob/master/translations/pt-BR.md)

  - [Simplified Chinese](https://github.com/uohzxela/clean-code-ruby/blob/master/translations/zh-CN.md)



**[⬆ back to top](#table-of-contents)**