Coding Standards Updates for PHP 5.6

With the minimum PHP version increasing to 5.6 as of WordPress 5.2, now’s a good time to be reviewing the WordPress Coding Standards.

Here is a set of changes that I’d like to propose.

Anonymous Functions (Closures)

Anonymous functions are a useful way to keep short logic blocks inline with a related function call. For example, this preg_replace_callback() call could be written like so:

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

This improves the readability of the codebase, as the developer doesn’t need to jump around the file to see what’s happening.

Coding Standards Proposal

Where the developer feels is appropriate, anonymous functions may be used as an alternative to creating new functions to pass as callbacks.

Anonymous functions must not be passed as filter or action callbacks in WordPress Core, as they cannot be removed by remove_action() / remove_filter() (see #46635 for a proposal to address this). Outside of Core, developers may pass anonymous functions as filter or action callbacks at their own discretion.


Namespaces are a neat way to encapsulate functionality, and are a common feature in modern PHP development practices. As we’ve discovered in the past, however, introducing namespaces to the WordPress codebase is a difficult problem, which will require careful architecture and implementation.

Side note: there’s currently no timeline for introducing namespaces to WordPress Core, expressions of interest are welcome. 🙂

Coding Standards Proposal

At this time, namespaces must not be used in WordPress Core.

Short Array Syntax

Rather than declaring arrays using the array( 1, 2, 3 ) syntax, they can now be shortened to [ 1, 2, 3 ]. This matches how arrays are declared in the WordPress JavaScript Coding Standards.

To allow for plugins and themes that support older versions of WordPress, I’d like to propose that WordPress Core switches to short array syntax immediately, but plugins and themes may choose which they use. A future iteration would make short array syntax a requirement.

Coding Standards Proposal

Arrays must be declared using short array syntax in WordPress Core. Arrays may be declared using short array syntax outside of Core.

Short Ternary Syntax

A fairly common pattern when setting a variable’s value looks something like this:

$a = $b ? $b : $c;

The short ternary syntax allows this to be shortened, like so:

$a = $b ?: $c;

It’s important to note that this is different to the null coalesce operator, which was added in PHP 7. If $b is undefined, the short ternary syntax will emit a notice.

Coding Standards Proposal

Short ternary syntax may be used where appropriate.

Assignments within conditionals

While this isn’t directly related to the PHP version bump, I’d like to propose disallowing assignments within conditionals. Particularly when there are multiple conditions, it can be quite difficult to spot assignments occurring in a conditional. This arguably falls under the Clever Code guidelines, but hasn’t been formalised.

For example, this if statement would be written like so:

$sticky_posts = get_option( 'sticky_posts' );
if ( 'post' === $post_type &amp;&amp; $sticky_posts ) {
	// ...

Coding Standards Proposal

Assignments within conditionals are not allowed.

Other New Features

Any other new features available in PHP 5.6 can be used, though we should continue to carefully consider their value and (in the case of newer PHP modules) availability on all hosts.

How do you feel about these changes? Are there other changes related to PHP 5.6 that you’d like to suggest?

#php, #wpcs