Functions
Name
Function names should say what they do
Bad:
class Email
{
//...
public function handle(): void
{
mail($this->to, $this->subject, $this->body);
}
}
$message = new Email(...);
// What is this? A handle for the message? Are we writing to a file now?
$message->handle();
Good:
class Email
{
//...
public function send(): void
{
mail($this->to, $this->subject, $this->body);
}
}
$message = new Email(...);
// Clear and obvious
$message->send();
Arguments
4 or fewer ideally.
Limiting the amount of function parameters is incredibly important because it makes testing your function easier. Having more than three leads to a combinatorial explosion where you have to test tons of different cases with each separate argument.
Zero arguments is the ideal case. One or two arguments is ok, and three should be avoided. Anything more than that should be consolidated. Usually, if you have more than two arguments then your function 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.
Bad:
class Questionnaire
{
public function __construct(
string $firstname,
string $lastname,
string $patronymic,
string $region,
string $district,
string $city,
string $phone,
string $email
) {
// ...
}
}
Good:
class Name
{
private $firstname;
private $lastname;
private $patronymic;
public function __construct(string $firstname, string $lastname, string $patronymic)
{
$this->firstname = $firstname;
$this->lastname = $lastname;
$this->patronymic = $patronymic;
}
// getters ...
}
class City
{
private $region;
private $district;
private $city;
public function __construct(string $region, string $district, string $city)
{
$this->region = $region;
$this->district = $district;
$this->city = $city;
}
// getters ...
}
class Contact
{
private $phone;
private $email;
public function __construct(string $phone, string $email)
{
$this->phone = $phone;
$this->email = $email;
}
// getters ...
}
class Questionnaire
{
public function __construct(Name $name, City $city, Contact $contact)
{
// ...
}
}
Abstraction
Functions should only be one level of abstraction When you have more than one level of abstraction your function is usually doing too much. Splitting up functions leads to reusability and easier testing.
Bad:
function parseBetterPHPAlternative(string $code): void
{
$regexes = [
// ...
];
$statements = explode(' ', $code);
$tokens = [];
foreach ($regexes as $regex) {
foreach ($statements as $statement) {
// ...
}
}
$ast = [];
foreach ($tokens as $token) {
// lex...
}
foreach ($ast as $node) {
// parse...
}
}
Bad too: We have carried out some of the functionality, but the parseBetterPHPAlternative() function is still very complex and not testable.
function tokenize(string $code): array
{
$regexes = [
// ...
];
$statements = explode(' ', $code);
$tokens = [];
foreach ($regexes as $regex) {
foreach ($statements as $statement) {
$tokens[] = /* ... */;
}
}
return $tokens;
}
function lexer(array $tokens): array
{
$ast = [];
foreach ($tokens as $token) {
$ast[] = /* ... */;
}
return $ast;
}
function parseBetterPHPAlternative(string $code): void
{
$tokens = tokenize($code);
$ast = lexer($tokens);
foreach ($ast as $node) {
// parse...
}
}
Good: The best solution is move out the dependencies of parseBetterPHPAlternative() function.
class Tokenizer
{
public function tokenize(string $code): array
{
$regexes = [
// ...
];
$statements = explode(' ', $code);
$tokens = [];
foreach ($regexes as $regex) {
foreach ($statements as $statement) {
$tokens[] = /* ... */;
}
}
return $tokens;
}
}
class Lexer
{
public function lexify(array $tokens): array
{
$ast = [];
foreach ($tokens as $token) {
$ast[] = /* ... */;
}
return $ast;
}
}
class BetterPHPAlternative
{
private $tokenizer;
private $lexer;
public function __construct(Tokenizer $tokenizer, Lexer $lexer)
{
$this->tokenizer = $tokenizer;
$this->lexer = $lexer;
}
public function parse(string $code): void
{
$tokens = $this->tokenizer->tokenize($code);
$ast = $this->lexer->lexify($tokens);
foreach ($ast as $node) {
// parse...
}
}
}
Flags
Don't use flags as function parameters Flags tell your user that this function does more than one thing. Functions should do one thing. Split out your functions if they are following different code paths based on a boolean.
Bad: ::code-group
function createFile(string $name, bool $temp = false): void
{
if ($temp) {
touch('./temp/'.$name);
} else {
touch($name);
}
}
::
Good:
function createFile(string $name): void
{
touch($name);
}
function createTempFile(string $name): void
{
touch('./temp/'.$name);
}
Avoid Side Effects
A function produces a side effect if it does anything other than take a value in and return another value or 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 functions 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: ::code-group
// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
$name = 'Ryan McDermott';
function splitIntoFirstAndLastName(): void
{
global $name;
$name = explode(' ', $name);
}
splitIntoFirstAndLastName();
var_dump($name); // ['Ryan', 'McDermott'];
::
Good:
function splitIntoFirstAndLastName(string $name): array
{
return explode(' ', $name);
}
$name = 'Ryan McDermott';
$newName = splitIntoFirstAndLastName($name);
var_dump($name); // 'Ryan McDermott';
var_dump($newName); // ['Ryan', 'McDermott'];
Names should describe side effects
Names should describe everything that a function, variable, or class is or does. Don’t hide side effects with a name. Don’t use a simple verb to describe a function that does more than just that simple action.
Bad:
public function getProfile(): Profile
{
if ($this->profile === null) {
$this->profile = new Profile($this);
$this->save();
}
return $this->profile;
}
Good:
public function createOrReturnProfile(): Profile
{
if ($this->profile === null) {
$this->profile = new Profile($this);
$this->save();
}
return $this->profile;
}
Globals
Don't write to global functions Polluting globals is a bad practice in many languages because you could clash with another library and the user of your API would be none-the-wiser until they get an exception in production. Let's think about an example: what if you wanted to have configuration array? You could write global function like config(), but it could clash with another library that tried to do the same thing.
Bad:
function config(): array
{
return [
'foo' => 'bar',
];
}
Good:
class Configuration
{
private $configuration = [];
public function __construct(array $configuration)
{
$this->configuration = $configuration;
}
public function get(string $key): ?string
{
// null coalescing operator
return $this->configuration[$key] ?? null;
}
}
Load configuration and create instance of Configuration class
$configuration = new Configuration([
'foo' => 'bar',
]);
And now you must use instance of Configuration in your application.
Singleton
Singleton is an anti-pattern. Paraphrased from Brian Button:
They are generally used as a global instance, why is that so bad? Because you hide the dependencies of your application in your code, instead of exposing them through the interfaces. Making something global to avoid passing it around is a code smell. They violate the single responsibility principle: by virtue of the fact that they control their own creation and lifecycle. They inherently cause code to be tightly coupled. This makes faking them out under test rather difficult in many cases. They carry state around for the lifetime of the application. Another hit to testing since you can end up with a situation where tests need to be ordered which is a big no for unit tests. Why? Because each unit test should be independent from the other. There is also very good thoughts by Misko Hevery about the root of problem.
Bad:
class DBConnection
{
private static $instance;
private function __construct(string $dsn)
{
// ...
}
public static function getInstance(): DBConnection
{
if (self::$instance === null) {
self::$instance = new self();
}
return self::$instance;
}
// ...
}
$singleton = DBConnection::getInstance();
Good:
class DBConnection
{
public function __construct(string $dsn)
{
// ...
}
// ...
}
Create instance of DBConnection class and configure it with DSN.
$connection = new DBConnection($dsn);
Conditionals
Encapsulate conditionals
Bad:
if ($article->state === 'published') {
// ...
}
Good:
if ($article->isPublished()) {
// ...
}
Avoid negative conditionals
Bad:
function isDOMNodeNotPresent(\DOMNode $node): bool
{
// ...
}
if (!isDOMNodeNotPresent($node))
{
// ...
}
Good:
function isDOMNodePresent(\DOMNode $node): bool
{
// ...
}
if (isDOMNodePresent($node)) {
// ...
}
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 function should only do one thing. When you have classes and functions that have if statements, you are telling your user that your function does more than one thing. Remember, just do one thing.
Bad:
class Airplane
{
// ...
public function getCruisingAltitude(): int
{
switch ($this->type) {
case '777':
return $this->getMaxAltitude() - $this->getPassengerCount();
case 'Air Force One':
return $this->getMaxAltitude();
case 'Cessna':
return $this->getMaxAltitude() - $this->getFuelExpenditure();
}
}
}
Good:
interface Airplane
{
// ...
public function getCruisingAltitude(): int;
}
class Boeing777 implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude() - $this->getPassengerCount();
}
}
class AirForceOne implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude();
}
}
class Cessna implements Airplane
{
// ...
public function getCruisingAltitude(): int
{
return $this->getMaxAltitude() - $this->getFuelExpenditure();
}
}
Type Checking
Avoid type-checking
PHP is untyped, which means your functions can take any type of argument. Sometimes you are bitten by this freedom and it becomes tempting to do type-checking in your functions. There are many ways to avoid having to do this. The first thing to consider is consistent APIs.
Bad:
function travelToTexas($vehicle): void
{
if ($vehicle instanceof Bicycle) {
$vehicle->pedalTo(new Location('texas'));
} elseif ($vehicle instanceof Car) {
$vehicle->driveTo(new Location('texas'));
}
}
Good:
function travelToTexas(Vehicle $vehicle): void
{
$vehicle->travelTo(new Location('texas'));
}
If you are working with basic primitive values like strings, integers, and arrays, and you use PHP 7+ and you can't use polymorphism but you still feel the need to type-check, you should consider type declaration or strict mode. It provides you with static typing on top of standard PHP syntax. The problem with manually type-checking is that doing it will require so much extra verbiage that the faux "type-safety" you get doesn't make up for the lost readability. Keep your PHP clean, write good tests, and have good code reviews. Otherwise, do all of that but with PHP strict type declaration or strict mode.
Bad:
function combine($val1, $val2): int
{
if (!is_numeric($val1) || !is_numeric($val2)) {
throw new \Exception('Must be of type Number');
}
return $val1 + $val2;
}
Good:
function combine(int $val1, int $val2): int
{
return $val1 + $val2;
}
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:
function oldRequestModule(string $url): void
{
// ...
}
function newRequestModule(string $url): void
{
// ...
}
$request = newRequestModule($requestUrl);
inventoryTracker('apples', $request, 'www.inventory-awesome.io');
Good:
function requestModule(string $url): void
{
// ...
}
$request = requestModule($requestUrl);
inventoryTracker('apples', $request, 'www.inventory-awesome.io');