php.md

# PHP Coding Standards

These PHP coding standards are intended for the WordPress community as a whole. They are mandatory for WordPress Core and we encourage you to use them for your themes and plugins as well.

While themes and plugins may choose to follow a different _coding style_, these **_coding standards_** are not just about _code style_, but also encompass established best practices regarding interoperability, translatability, and security in the WordPress ecosystem, so, even when using a different _code style_, we recommend you still adhere to the WordPress Coding Standards in regard to these best practices.

While not all code may fully comply with these standards (yet), all newly committed and/or updated code should fully comply with these coding standards.

Also see the [PHP Inline Documentation Standards](https://developer.wordpress.org/coding-standards/inline-documentation-standards/php/) for further guidelines.

If you want to automatically check your code against this standard, you can use the official [WordPress Coding Standards](https://github.com/WordPress/WordPress-Coding-Standards) tooling, which is run using [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer/).

## General

### Opening and Closing PHP Tags

When embedding multi-line PHP snippets within an HTML block, the PHP open and close tags must be on a line by themselves.

Correct (Multiline):

```php
function foo() {
    ?>
    <div>
        <?php
        echo esc_html(
            bar(
                $baz,
                $bat
            )
        );
        ?>
    </div>
    <?php
}
```

Correct (Single Line):

```php
<input name="<?php echo esc_attr( $name ); ?>" />
```

Incorrect:

```php
if ( $a === $b ) { ?>
<some html>
<?php }
```

### No Shorthand PHP Tags

**Important:** Never use shorthand PHP start tags. Always use full PHP tags.

Correct:

```php
<?php ... ?>
<?php echo esc_html( $var ); ?>
```

Incorrect:

```php
<? ... ?>
<?= esc_html( $var ) ?>
```

### Single and Double Quotes

Use single and double quotes when appropriate. If you're not evaluating anything in the string, use single quotes. You should almost never have to escape quotes in a string, because you can just alternate your quoting style, like so:

```php
echo '<a href="/static/link" class="button button-primary">Link name</a>';
echo "<a href='{$escaped_link}'>text with a ' single quote</a>";
```

Text that goes into HTML or XML attributes should be escaped so that single or double quotes do not end the attribute value and invalidate the HTML, causing a security issue. See [Data Validation](https://developer.wordpress.org/plugins/security/data-validation/) in the Plugin Handbook for further details.

## Naming

### Naming Conventions

Use lowercase letters in variable, action/filter, and function names (never `camelCase`). Separate words via underscores. Don't abbreviate variable names unnecessarily; let the code be unambiguous and self-documenting.

```php
function some_name( $some_variable ) { [...] }
```

Class names should use capitalized words separated by underscores. Any acronyms should be all upper case.

```php
class Walker_Category extends Walker { [...] }
class WP_HTTP { [...] }
```

Constants should be in all upper-case with underscores separating words:

```php
define( 'DOING_AJAX', true );
```

Files should be named descriptively using lowercase letters. Hyphens should separate words.

```php
my-plugin-name.php
```

Class file names should be based on the class name with `class-` prepended and the underscores in the class name replaced with hyphens, for example, `WP_Error` becomes:

```php
class-wp-error.php
```

This file-naming standard is for all current and new files with classes. There is one exception to this rule for three legacy files: `class.wp-dependencies.php`, `class.wp-scripts.php`, `class.wp-styles.php`. Those files are prepended with `class.`, a dot after the word class instead of a hyphen.

Files containing template tags in the `wp-includes` directory should have `-template` appended to the end of the name so that they are obvious.

```php
general-template.php
```

### Interpolation for Naming Dynamic Hooks

Dynamic hooks should be named using interpolation rather than concatenation for readability and discoverability purposes.

Dynamic hooks are hooks that include dynamic values in their tag name, e.g. `{$new_status}_{$post->post_type}` (publish_post).

Variables used in hook tags should be wrapped in curly braces `{` and `}`, with the complete outer tag name wrapped in double quotes. This is to ensure PHP can correctly parse the given variables' types within the interpolated string.

```php
do_action( "{$new_status}_{$post->post_type}", $post->ID, $post );
```

Where possible, dynamic values in tag names should also be as succinct and to the point as possible. `$user_id` is much more self-documenting than, say, `$this->id`.

## Whitespace

### Space Usage

Always put spaces after commas, and on both sides of logical, comparison, string and assignment operators.

```php
SOME_CONST === 23;
foo() && bar();
! $foo;
array( 1, 2, 3 );
$baz . '-5';
$term .= 'X';
```

Put spaces on both sides of the opening and closing parentheses of control structure blocks.

```php
foreach ( $foo as $bar ) { ...
```

When defining a function, do it like so:

```php
function my_function( $param1 = 'foo', $param2 = 'bar' ) { ...

function my_other_function() { ...
```

When calling a function, do it like so:

```php
my_function( $param1, func_param( $param2 ) );
my_other_function();
```

When performing logical comparisons, do it like so:

```php
if ( ! $foo ) { ...
```

[Type casts](https://www.php.net/manual/en/language.types.type-juggling.php#language.types.typecasting) must be lowercase. Always prefer the short form of type casts, `(int)` instead of `(integer)` and `(bool)` rather than `(boolean)`. For float casts use `(float)`, not `(real)` which is [deprecated](https://www.php.net/manual/en/migration74.deprecated.php#migration74.deprecated.core.real) in PHP 7.4, and removed in PHP 8:

```php
foreach ( (array) $foo as $bar ) { ...

$foo = (bool) $bar;
```

When referring to array items, only include a space around the index if it is a variable, for example:

```php
$x = $foo['bar']; // Correct.
$x = $foo[ 'bar' ]; // Incorrect.

$x = $foo[0]; // Correct.
$x = $foo[ 0 ]; // Incorrect.

$x = $foo[ $bar ]; // Correct.
$x = $foo[$bar]; // Incorrect.
```

In a `switch` block, there must be no space between the `case` condition and the colon.

```php
switch ( $foo ) {
    case 'bar': // Correct.
    case 'ba' : // Incorrect.
}
```

Similarly, there should be no space before the colon on return type declarations.

```php
function sum( $a, $b ): float {
    return $a + $b;
}
```

Unless otherwise specified, parentheses should have spaces inside them.

```php
if ( $foo && ( $bar || $baz ) ) { ...

my_function( ( $x - 1 ) * 5, $y );
```

### Indentation

Your indentation should always reflect logical structure. Use **real tabs**, **not spaces**, as this allows the most flexibility across clients.

Exception: if you have a block of code that would be more readable if things are aligned, use spaces:

```php
[tab]$foo   = 'somevalue';
[tab]$foo2  = 'somevalue2';
[tab]$foo34 = 'somevalue3';
[tab]$foo5  = 'somevalue4';
```

For associative arrays, _each item_ should start on a new line when the array contains more than one item:

```php
$query = new WP_Query( array( 'ID' => 123 ) );
```

```php
$args = array(
[tab]'post_type'   => 'page',
[tab]'post_author' => 123,
[tab]'post_status' => 'publish',
);
 
$query = new WP_Query( $args );
```

Note the comma after the last array item: this is recommended because it makes it easier to change the order of the array, and makes for cleaner diffs when new items are added.

```php
$my_array = array(
[tab]'foo'   => 'somevalue',
[tab]'foo2'  => 'somevalue2',
[tab]'foo3'  => 'somevalue3',
[tab]'foo34' => 'somevalue3',
);
```

For `switch` control structures, `case` statements should be indented one tab from the `switch` statement and the contents of the `case` should be indented one tab from the `case` condition statement.

```php
switch ( $type ) {
[tab]case 'foo':
[tab][tab]some_function();
[tab][tab]break;
[tab]case 'bar':
[tab][tab]some_function();
[tab][tab]break;
}
```

**Rule of thumb:** Tabs should be used at the beginning of the line for indentation, while spaces can be used mid-line for alignment.

### Remove Trailing Spaces

Remove trailing whitespace at the end of each line. Omitting the closing PHP tag at the end of a file is preferred. If you use the tag, make sure you remove trailing whitespace.

## Formatting

### Brace Style

Braces shall be used for all blocks in the style shown here:

```php
if ( condition ) {
    action1();
    action2();
} elseif ( condition2 && condition3 ) {
    action3();
    action4();
} else {
    defaultaction();
}
```

If you have a really long block, consider whether it can be broken into two or more shorter blocks, functions, or methods, to reduce complexity, improve ease of testing, and increase readability.

Braces should always be used, even when they are not required:

```php
if ( condition ) {
    action0();
}

if ( condition ) {
    action1();
} elseif ( condition2 ) {
    action2a();
    action2b();
}

foreach ( $items as $item ) {
    process_item( $item );
}
```

Note that requiring the use of braces means that _single-statement inline control structures_ are prohibited. You are free to use the [alternative syntax for control structures](https://www.php.net/manual/en/control-structures.alternative-syntax.php) (e.g. `if`/`endif`, `while`/`endwhile`)—especially in templates where PHP code is embedded within HTML, for instance:

```php
<?php if ( have_posts() ) : ?>
    <div class="hfeed">
        <?php while ( have_posts() ) : the_post(); ?>
            <article id="<?php echo esc_attr( 'post-' . get_the_ID() ); ?>" class="<?php echo esc_attr( get_post_class() ); ?>">
                <!-- ... -->
            </article>
        <?php endwhile; ?>
    </div>
<?php endif; ?>
```

### Declaring Arrays

Using long array syntax ( `array( 1, 2, 3 )` ) for declaring arrays is generally more readable than short array syntax ( `[ 1, 2, 3 ]` ), particularly for those with vision difficulties. Additionally, it's much more descriptive for beginners.

Arrays must be declared using long array syntax.

### Multiline Function Calls

When splitting a function call over multiple lines, each parameter must be on a separate line. Single line inline comments can take up their own line.

Each parameter must take up no more than a single line. Multi-line parameter values must be assigned to a variable and then that variable should be passed to the function call.

```php
$bar = array(
    'use_this' => true,
    'meta_key' => 'field_name',
);
$baz = sprintf(
    /* translators: %s: Friend's name */
    __( 'Hello, %s!', 'yourtextdomain' ),
    $friend_name
);

$a = foo(
    $bar,
    $baz,
    /* translators: %s: cat */
    sprintf( __( 'The best pet is a %s.' ), 'cat' )
);
```

## Object-Oriented Programming

### Only One Object Structure (Class/Interface/Trait) per File

For instance, if we have a file called `class-example-class.php` it can only contain one class in that file.

```php
// Incorrect: file class-example-class.php.
class Example_Class { [...] }

class Example_Class_Extended { [...] }
```

The second class should be in its own file called `class-example-class-extended.php`.

```php
// Correct: file class-example-class.php.
class Example_Class { [...] }
```

```php
// Correct: file class-example-class-extended.php.
class Example_Class_Extended { [...] }
```

## Control Structures

### Use `elseif`, not `else if`

`else if` is not compatible with the colon syntax for `if|elseif` blocks. For this reason, use `elseif` for conditionals.

### Yoda Conditions

```php
if ( true === $the_force ) {
    $victorious = you_will( $be );
}
```

When doing logical comparisons involving variables, always put the variable on the right side and put constants, literals, or function calls on the left side. If neither side is a variable, the order is not important. (In [computer science terms](https://en.wikipedia.org/wiki/Value_(computer_science)#Assignment:_l-values_and_r-values), in comparisons always try to put l-values on the right and r-values on the left.)

In the above example, if you omit an equals sign (admit it, it happens even to the most seasoned of us), you'll get a parse error, because you can't assign to a constant like `true`. If the statement were the other way around `( $the_force = true )`, the assignment would be perfectly valid, returning `1`, causing the if statement to evaluate to `true`, and you could be chasing that bug for a while.

A little bizarre, it is, to read. Get used to it, you will.

This applies to `==`, `!=`, `===`, and `!==`. Yoda conditions for `<`, `>`, `<=` or `>=` are significantly more difficult to read and are best avoided.

## Operators

### Ternary Operator

[Ternary operators](https://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary) are fine, but always have them test if the statement is true, not false. Otherwise, it just gets confusing. (An exception would be using `! empty()`, as testing for false here is generally more intuitive.)

The short ternary operator must not be used.

For example:

```php
// (if statement is true) ? (do this) : (else, do this);
$musictype = ( 'jazz' === $music ) ? 'cool' : 'blah';
// (if field is not empty ) ? (do this) : (else, do this);
```

### Error Control Operator `@`

As noted in the [PHP docs](https://www.php.net/manual/en/language.operators.errorcontrol.php):

> PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any diagnostic error that might be generated by that expression will be suppressed.

While this operator does exist in Core, it is often used lazily instead of doing proper error checking. Its use is highly discouraged, as even the PHP docs also state:

> Warning: Prior to PHP 8.0.0, it was possible for the @ operator to disable critical errors that will terminate script execution. For example, prepending @ to a call of a function that did not exist, by being unavailable or mistyped, would cause the script to terminate with no indication as to why.

## Database

### Database Queries

Avoid touching the database directly. If there is a defined function that can get the data you need, use it. Database abstraction (using functions instead of queries) helps keep your code forward-compatible and, in cases where results are cached in memory, it can be many times faster.

If you must touch the database, consider creating a [Trac](https://core.trac.wordpress.org/) ticket. There you can discuss the possibility of adding a new function to cover the functionality you wanted, for a future version of WordPress.

### Formatting SQL statements

When formatting SQL statements you may break them into several lines and indent if it is sufficiently complex to warrant it. Most statements work well as one line though. Always capitalize the SQL parts of the statement like `UPDATE` or `WHERE`.

Functions that update the database should expect their parameters to lack SQL slash escaping when passed. Escaping should be done as close to the time of the query as possible, preferably by using `$wpdb->prepare()`

`$wpdb->prepare()` is a method that handles escaping, quoting, and int-casting for SQL queries. It uses a subset of the `sprintf()` style of formatting. Example :

```php
$var = "dangerous'"; // Raw data that may or may not need to be escaped.
$id = some_foo_number(); // Data we expect to be an integer, but we're not certain.

$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET post_title = %s WHERE ID = %d", $var, $id ) );
```

`%s` is used for string placeholders and `%d` is used for integer placeholders. Note that they are not 'quoted'! `$wpdb->prepare()` will take care of escaping and quoting for us. The benefit of this is that it is easy to see at a glance whether something has been escaped or not because it happens right when the query happens.

See [Data Validation](https://developer.wordpress.org/plugins/security/data-validation/) in the Plugin Handbook for further details.

## Recommendations

### Self-Explanatory Flag Values for Function Arguments

Prefer string values to just `true` and `false` when calling functions.

```php
// Incorrect.
function eat( $what, $slowly = true ) {
...
}
eat( 'mushrooms' );
eat( 'mushrooms', true ); // What does true mean?
eat( 'dogfood', false ); // What does false mean? The opposite of true?
```

PHP only supports named arguments as of PHP 8.0. However, as WordPress currently still supports older PHP versions, we cannot yet use those.
Without named arguments, the values of the flags are meaningless, and each time we come across a function call like the examples above, we have to search for the function definition. The code can be made more readable by using descriptive string values, instead of booleans.

```php
// Correct.
function eat( $what, $speed = 'slowly' ) {
...
}
eat( 'mushrooms' );
eat( 'mushrooms', 'slowly' );
eat( 'dogfood', 'quickly' );
```

When more words are needed to describe the function parameters, an `$args` array may be a better pattern.

```php
function eat( $what, $args ) {
...
}
eat ( 'noodles', array( 'speed' => 'moderate' ) );
```

Be careful when using this pattern, as it can lead to "Undefined array index" notices if input isn't validated before use. Use this pattern only where it makes sense (i.e. multiple possible arguments), not just for the sake of it.

### Clever Code

In general, readability is more important than cleverness or brevity.

```php
isset( $var ) || $var = some_function();
```

Although the above line is clever, it takes a while to grok if you're not familiar with it. So, just write it like this:

```php
if ( ! isset( $var ) ) {
    $var = some_function();
}
```

Unless absolutely necessary, loose comparisons should not be used, as their behaviour can be misleading.

Correct:

```php
if ( 0 === strpos( $text, 'WordPress' ) ) {
    echo esc_html__( 'Yay WordPress!', 'textdomain' );
}
```

Incorrect:

```php
if ( 0 == strpos( 'WordPress', 'foo' ) ) {
    echo esc_html__( 'Yay WordPress!', 'textdomain' );
}
```

Assignments must not be placed in conditionals.

Correct:

```php
$data = $wpdb->get_var( '...' );
if ( $data ) {
    // Use $data.
}
```

Incorrect:

```php
if ( $data = $wpdb->get_var( '...' ) ) {
    // Use $data.
}
```

In a `switch` statement, it's okay to have multiple empty cases fall through to a common block. If a case contains a block, then falls through to the next block, however, this must be explicitly commented.

```php
switch ( $foo ) {
    case 'bar':                // Correct, an empty case can fall through without comment.
    case 'baz':
        echo esc_html( $foo ); // Incorrect, a case with a block must break, return, or have a comment.
    case 'cat':
        echo 'mouse';
        break;                 // Correct, a case with a break does not require a comment.
    case 'dog':
        echo 'horse';
        // no break            // Correct, a case can have a comment to explicitly mention the fall through.
    case 'fish':
        echo 'bird';
        break;
}
```

The `goto` statement must never be used.

The `eval()` construct is _very dangerous_ and is impossible to secure. Additionally, the `create_function()` function, which internally performs an `eval()`, is deprecated since PHP 7.2 and has been removed in PHP 8.0. Neither of these must be used.

### Closures (Anonymous Functions)

Where appropriate, closures may be used as an alternative to creating new functions to pass as callbacks. For example:

```php
$caption = preg_replace_callback(
    '/<[a-zA-Z0-9]+(?: [^<>]+>)*/',
    function ( $matches ) {
        return preg_replace( '/[\r\n\t]+/', ' ', $matches[0] );
    },
    $caption
);
```

Closures should not be passed as filter or action callbacks, as removing these via `remove_action()` / `remove_filter()` is complex (at this time)  (see [#46635](https://core.trac.wordpress.org/ticket/46635 "Improve identifying of non–trivial callbacks in hooks") for a proposal to address this).

### Regular Expressions

Perl compatible regular expressions ([PCRE](https://www.php.net/pcre), `preg_` functions) should be used in preference to their POSIX counterparts. Never use the `/e` switch, use `preg_replace_callback` instead.

It's most convenient to use single-quoted strings for regular expressions since, contrary to double-quoted strings, they have only two metasequences which need escaping: `\'` and `\\`.

### Don't `extract()`

Per [#22400](https://core.trac.wordpress.org/ticket/22400 "Remove all, or at least most, uses of extract() within WordPress"):

> `extract()` is a terrible function that makes code harder to debug and harder to understand. We should discourage it's [sic] use and remove all of our uses of it.

Joseph Scott has [a good write-up of why it's bad](https://blog.josephscott.org/2009/02/05/i-dont-like-phps-extract-function/).