PSR Catalog

PSR Catalog

The PSR Catalog: Interfaces Worth Implementing

Most PSRs are small interfaces in psr/* packages: code that type-hints Psr\Log\LoggerInterface accepts Monolog 21,402 or any other logger. Statuses are from php-fig.org:

Key PSRs and their status (September 2026)
PSR	Subject	Status	You meet it in
1	Basic coding standard	Accepted	Naming (Coding Standards)
3	Logger interface	Accepted	Monolog (Monolog)
4	Autoloading	Accepted	Composer 5,243 (PSR-4 and Directory Layout)
7	HTTP messages	Accepted	Guzzle 23,452 , Slim 32,516
11	Container interface	Accepted	DI containers (Dependency Injection)
12	Extended coding style	Accepted; PER-CS replaces it	Formatters
15	HTTP handlers, middleware	Accepted	Mezzio, Slim
17	HTTP factories	Accepted	Building PSR-7 objects
18	HTTP client	Accepted	Guzzle 7+
20	Clock	Accepted	Testable time

PSR-0 and PSR-2 are deprecated; PSR-5 and PSR-19 (PHPDoc) are drafts. PSR-20 (composer require psr/clock) is the easiest win: code that asks a clock for the time is testable.

PSR-20: a sale banner checked against a frozen clock (clock.php)PHP

<?php
require __DIR__ . '/vendor/autoload.php';
final readonly class FrozenClock implements Psr\Clock\ClockInterface {      // PSR-20
  public function __construct(private DateTimeImmutable $at) {}
  public function now(): DateTimeImmutable { return $this->at; }
}
function banner(Psr\Clock\ClockInterface $clock): string {
  return $clock->now() < new DateTimeImmutable('2026-12-01') ? 'Autumn sale' : '';
}
var_dump(banner(new FrozenClock(new DateTimeImmutable('2026-11-30 23:59'))),
  banner(new FrozenClock(new DateTimeImmutable('2026-12-01 00:00'))));

Output

string(11) "Autumn sale"
string(0) ""

In production, pass a real-time clock such as symfony/clock's NativeClock.

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