PSR-6: Caching Interface

Also Known As

TL;DR

Explanation

PSR-6 defines two interfaces: CacheItemPoolInterface (the cache driver — get, save, deleteItem, clear, commit) and CacheItemInterface (a cache entry — get/set value, expiry). By type-hinting CacheItemPoolInterface, application code is decoupled from the specific backend (Redis, Memcached, APCu, filesystem). Symfony Cache is the canonical implementation, supporting all backends with a unified API. PSR-16 (Simple Cache) provides a simpler single-class alternative for basic get/set/delete use cases that don't need the item object model. Libraries should accept PSR-6 or PSR-16 interfaces rather than concrete cache clients.

Common Misconception

Why It Matters

Common Mistakes

• Using cache library APIs directly instead of PSR-6 — locks the codebase to one cache implementation.
• Not checking CacheItem::isHit() — treating a miss as a hit returns stale null data.
• Not setting expiry on cache items — items live forever until manually deleted or evicted.
• Serializing objects manually before caching instead of letting PSR-6 handle serialization.

Code Examples

// Direct Redis dependency — cannot swap to file cache:
$redis = new Redis();
$redis->get('user:' . $id);

// PSR-6 — swappable:
function getUser(CacheItemPoolInterface $cache, int $id): User {
    $item = $cache->getItem('user:' . $id);
    if (!$item->isHit()) {
        $item->set(User::find($id))->expiresAfter(300);
        $cache->save($item);
    }
    return $item->get();
}

// PSR-6 Caching Interface
use Psr\Cache\CacheItemPoolInterface;
use Psr\Cache\CacheItemInterface;

// Writing to cache
\$item = \$cache->getItem('user:' . \$userId);
if (!\$item->isHit()) {
    \$user = \$this->db->fetchUser(\$userId);
    \$item->set(\$user)->expiresAfter(3600);
    \$cache->save(\$item);
} else {
    \$user = \$item->get();
}

// Delete
\$cache->deleteItem('user:' . \$userId);

// PSR-6 compatible implementations:
// symfony/cache, cache/filesystem-adapter, league/flysystem-cached-adapter

// PSR-16 (Simple Cache) — simpler interface:
// \$cache->get('key', 'default');
// \$cache->set('key', \$value, 3600);

References

• ↗ https://www.php-fig.org/psr/psr-6/

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