Yii2 Core framework code style

The following code style is used for Yii 2.x core and official extensions development. If you want to pull-request code into the core, consider using it. We aren't forcing you to use this code style for your application. Feel free to choose what suits you better.

You can get a config for CodeSniffer here: https://github.com/yiisoft/yii2-coding-standards

1. Overview

Overall we're using PSR-2 compatible style so everything that applies to PSR-2 is applied to our code style as well.

  • Files MUST use either <?php or <?= tags.
  • There should be a newline at the end of file.
  • Files MUST use only UTF-8 without BOM for PHP code.
  • Code MUST use 4 spaces for indenting, not tabs.
  • Class names MUST be declared in StudlyCaps.
  • Class constants MUST be declared in all upper case with underscore separators.
  • Method names MUST be declared in camelCase.
  • Property names MUST be declared in camelCase.
  • Property names MUST start with an initial underscore if they are private.
  • Always use elseif instead of else if.

2. Files

2.1. PHP Tags

  • PHP code MUST use <?php ?> or <?= tags; it MUST NOT use the other tag variations such as <?.
  • In case file contains PHP only it should not have trailing ?>.
  • Do not add trailing spaces to the end of the lines.
  • Any file that contains PHP code should end with the extension .php.

2.2. Character Encoding

PHP code MUST use only UTF-8 without BOM.

3. Class Names

Class names MUST be declared in StudlyCaps. For example, Controller, Model.

4. Classes

The term "class" refers to all classes and interfaces here.

  • Classes should be named using CamelCase.
  • The brace should always be written on the line underneath the class name.
  • Every class must have a documentation block that conforms to the PHPDoc.
  • All code in a class must be indented with a single tab.
  • There should be only one class in a single PHP file.
  • All classes should be namespaced.
  • Class name should match file name. Class namespace should match directory structure.
 * Documentation
class MyClass extends \yii\Object implements MyInterface
    // code

4.1. Constants

Class constants MUST be declared in all upper case with underscore separators. For example:

class Foo
    const VERSION = '1.0';
    const DATE_APPROVED = '2012-06-01';

4.2. Properties

  • When declaring public class members specify public keyword explicitly.
  • Public and protected variables should be declared at the top of the class before any method declarations. Private variables should also be declared at the top of the class but may be added right before the methods that are dealing with them in cases where they are only related to a small subset of the class methods.
  • The order of property declaration in a class should be ascending from public over protected to private.
  • For better readability there should be no blank lines between property declarations and two blank lines between property and method declaration sections.
  • Private variables should be named like $_varName.
  • Public class members and standalone variables should be named using $camelCase with first letter lowercase.
  • Use descriptive names. Variables such as $i and $j are better not to be used.

For example:

class Foo
    public $publicProp;
    protected $protectedProp;
    private $_privateProp;

4.3. Methods

  • Functions and methods should be named using camelCase with first letter lowercase.
  • Name should be descriptive by itself indicating the purpose of the function.
  • Class methods should always declare visibility using private, protected and public modifiers. var is not allowed.
  • Opening brace of a function should be on the line after the function declaration.
 * Documentation
class Foo
     * Documentation
    public function bar()
        // code
        return $value;

4.4 Doc blocks

@param, @var, @property and @return must declare types as boolean, integer, string, array or null. You can use a class names as well such as Model or ActiveRecord. For a typed arrays use ClassName[].

4.5 Constructors

  • __construct should be used instead of PHP 4 style constructors.


5.1 Types

  • All PHP types and values should be used lowercase. That includes true, false, null and array.

Changing type of an existing variable is considered as a bad practice. Try not to write such code unless it is really necessary.

public function save(Transaction $transaction, $argument2 = 100)
    $transaction = new Connection; // bad
    $argument2 = 200; // good

5.2 Strings

  • If string doesn't contain variables or single quotes, use single quotes.
$str = 'Like this.';
  • If string contains single quotes you can use double quotes to avoid extra escaping.

Variable substitution

$str1 = "Hello $username!";
$str2 = "Hello {$username}!";

The following is not permitted:

$str3 = "Hello ${username}!";


Add spaces around dot when concatenating strings:

$name = 'Yii' . ' Framework';

When string is long format is the following:

$sql = "SELECT *"
    . "FROM `post` "
    . "WHERE `id` = 121 ";

5.3 arrays

For arrays we're using PHP 5.4 short array syntax.

Numerically indexed

  • Do not use negative numbers as array indexes.

Use the following formatting when declaring array:

$arr = [3, 14, 15, 'Yii', 'Framework'];

If there are too many elements for a single line:

$arr = [
    3, 14, 15,
    92, 6, $test,
    'Yii', 'Framework',


Use the following format for associative arrays:

$config = [
    'name'  => 'Yii',
    'options' => ['usePHP' => true],

5.4 control statements

  • Control statement condition must have single space before and after parenthesis.
  • Operators inside of parenthesis should be separated by spaces.
  • Opening brace is on the same line.
  • Closing brace is on a new line.
  • Always use braces for single line statements.
if ($event === null) {
    return new Event();
if ($event instanceof CoolEvent) {
    return $event->instance();
return null;

// the following is NOT allowed:
if (!$model && null === $event)
    throw new Exception('test');

Prefer avoiding else after return where it makes sense. Use guard conditions.

$result = $this->getResult();
if (empty($result)) {
  return true;
} else {
  // process result

is better as

$result = $this->getResult();
if (empty($result)) {
  return true;

// process result


Use the following formatting for switch:

switch ($this->phpType) {
    case 'string':
        $a = (string) $value;
    case 'integer':
    case 'int':
        $a = (int) $value;
    case 'boolean':
        $a = (bool) $value;
        $a = null;

5.5 function calls

doIt(2, 3);

doIt(['a' => 'b']);

doIt('a', [
    'a' => 'b',
    'c' => 'd',

5.6 Anonymous functions (lambda) declarations

Note space between function/use tokens and open parenthesis:

// good
$n = 100;
$sum = array_reduce($numbers, function ($r, $x) use ($n) {
    $r += $x * $n;
    return $r;

// bad
$n = 100;
$mul = array_reduce($numbers, function($r, $x) use($n) {
    $r *= $x * $n;
    return $r;


  • Refer to phpDoc for documentation syntax.
  • Code without documentation is not allowed.
  • All class files must contain a "file-level" docblock at the top of each file and a "class-level" docblock immediately above each class.
  • There is no need to use @return if method does return nothing.
  • All virtual properties in classes that extend from yii\base\Object are documented with an @property tag in the class doc block. These annotations are automatically generated from the @return or @param tag in the corresponding getter or setter by running ./build php-doc in the build directory. You may add an @property tag to the getter or setter to explicitly give a documentation message for the property introduced by these methods when description differs from what is stated in @return. Here is an example:

php <?php /** * Returns the errors for all attribute or a single attribute. * @param string $attribute attribute name. Use null to retrieve errors for all attributes. * @property array An array of errors for all attributes. Empty array is returned if no error. * The result is a two-dimensional array. See [[getErrors()]] for detailed description. * @return array errors for all attributes or the specified attribute. Empty array is returned if no error. * Note that when returning errors for all attributes, the result is a two-dimensional array, like the following: * ... */ public function getErrors($attribute = null)


 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/


 * Component is the base class that provides the *property*, *event* and *behavior* features.
 * @include @yii/docs/base-Component.md
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
class Component extends \yii\base\Object

Function / method

 * Returns the list of attached event handlers for an event.
 * You may manipulate the returned [[Vector]] object by adding or removing handlers.
 * For example,
 * ~~~
 * $component->getEventHandlers($eventName)->insertAt(0, $eventHandler);
 * ~~~
 * @param string $name the event name
 * @return Vector list of attached event handlers for the event
 * @throws Exception if the event is not defined
public function getEventHandlers($name)
    if (!isset($this->_e[$name])) {
        $this->_e[$name] = new Vector;
    return $this->_e[$name];


As you can see in the examples above we use markdown to format the phpDoc comments.

There is additional syntax for cross linking between classes, methods and properties in the documentation:

  • '[[canSetProperty]] will create a link to the canSetProperty method or property of the same class.
  • '[[Component::canSetProperty]] will create a link to canSetProperty method of the class Component in the same namespace.
  • '[[yii\base\Component::canSetProperty]] will create a link to canSetProperty method of the class Component in namespace yii\base.
  • '[[Component]] will create a link to the Component class in the same namespace. Adding namespace to the class name is also possible here.

To give one of the above mentioned links another label than the class or method name you can use the syntax shown in the following example:

... as displayed in the [[header|header cell]].

The part before the | is the method, property or class reference while the part after | is the link label.

It is also possible to link to the Guide using the following syntax:

[link to guide](guide:file-name.md)
[link to guide](guide:file-name.md#subsection)


  • One-line comments should be started with // and not #.
  • One-line comment should be on its own line.

Additional rules

=== [] vs empty()

Use empty() where possible.

multiple return points

Return early when conditions nesting starts to get cluttered. If the method is short it doesn't matter.

self vs. static

Always use static except the following cases:

  • accessing constants MUST be done via self: self::MY_CONSTANT
  • accessing private static properties MUST be done via self: self::$_events
  • It is allowed to use self for recursion to call current implementation again instead of extending classes implementation.

value for "don't do something"

Properties allowing to configure component not to do something should accept value of false. null, '', or [] should not be assumed as such.

Directory/namespace names

  • use lower case
  • use plural form for nouns which represent objects (e.g. validators)
  • use singular form for names representing relevant functionality/features (e.g. web)