Use C::class instead of 'C' for strings holding class names

Problem/Motivation

State what you believe is wrong or missing from the current standards.

There are places in Drupal where we have string values referring to class names.

Often these values are initialized with regular string literals. This makes it hard for an IDE (I only tried with PhpStorm, no idea about others) to

• list these string literals in "find usages" for a class.
• provide auto-completion when writing this code.
• warn you about non-existing or misspelled classes.
• include these string literals in refactor/rename.

PHP provides a syntax where all this is supported: "::class".
I propose that this becomes the recommended way of referring to class names as strings.

Example

In Drupal\Core\Cache\ApcuBackendFactory::__construct():

Current code:

      $this->backendClass = 'Drupal\Core\Cache\ApcuBackend';

could be replaced with

      $this->backendClass = \Drupal\Core\Cache\ApcuBackend::class;

or better

[..]
use Drupal\Core\Cache\ApcuBackend;
[..]
      $this->backendClass = ApcuBackend::class;

Side note

The same problem exists with procedural callbacks, or string method names. Unfortunately there is no foo::function syntax in PHP. I personally always put a @see comment on top of string literals referring to functions or callbacks, to facilitate "find usages". But this should be dealt with in a separate issue.

Benefits

If we adopted this change, the Drupal Project would benefit by …

• … making it easier to find all usages of a class (in IDEs or similar).
• … providing auto-completion when writing this code.
• … warn you about non-existing or misspelled classes.
• … include these string literals in refactor/rename.

Three supporters required

1. https://www.drupal.org/u/drunken-monkey (2025-02-23)
2. https://www.drupal.org/u/borisson_ (2017-10-14)
3. https://www.drupal.org/u/quietone (2026-04-19)

Proposed changes

1. PHP coding standards

Current text

None (new section)

Proposed text

Referencing classes

Whenever a class is referenced directly in code, the Classname::class syntax should be used, as in these examples:

class_alias(TranslatableMarkup::class, TranslationWrapper::class, TRUE);
uasort($info, [SortArray::class, 'sortByWeightElement']);
protected readonly string $pluginDefinitionAttributeName = Plugin::class;

2. PHP coding standards » Constructor calls

Current text

Note that if the class name is a variable, the variable will be evaluated first to get the class name, and then the constructor will be called. Use the same syntax:

$bar = 'MyClassName';
$foo = new $bar();
$foo = new $bar($arg1, $arg2);

Proposed text

Note that if the class name is a variable, the variable will be evaluated first to get the class name, and then the constructor will be called. Use the same syntax:

$bar = MyClassName::class;
$foo = new $bar();
$foo = new $bar($arg1, $arg2);

Remaining tasks

1. Create this issue in the Coding Standards queue, using the defined template
2. Add supporters
3. Create a Change Record
4. Review by the Coding Standards Committee
5. Coding Standards Committee takes action as required
6. Discussed by the Core Committer Committee, if it impacts Drupal Core
7. Final review by Coding Standards Committee
8. Documentation updates
   1. Edit all pages
   2. Publish change record
   3. Remove 'Needs documentation edits' tag
9. If applicable, create follow-up issues for PHPCS rules/sniffs changes

For a full explanation of these steps see the Coding Standards project page