Simple cache interface idea

CacheInterface.php

<?php

namespace Psr\Cache

interface CacheInterface
{
    /**
     * @param string $key
     *   Key for the value in the cache.
     * @param bool $isHit
     *   Value is populated with `true` on hit or `false` on miss. This is
     *   a simple way to distinguish between falsey values and cache misses,
     *   such that race conditions can be avoided.
     *
     * @return mixed
     *   The cached value.
     * @throws CacheException
     *   If there was a problem retrieving the value from the cache.
     */
    public function get($key, &$isHit = null);

    /**
     * @param string $key
     *   Key for the value in the cache.
     *
     * @return bool
     *   Whether the value exists in the cache.
     * @throws CacheException
     *   If there was a problem checking if the value exists in the cache.
     */
    public function has($key);

    /**
     * @param string $key
     *   Key for the value in the cache.
     * @param mixed $value
     *   Value to cache.
     * @param int|\DateTime $ttl
     *   - If an integer is passed, it is interpreted as the number of seconds
     *     after which the item MUST be considered expired.
     *   - If a DateTime object is passed, it is interpreted as the point in
     *     time after which the item MUST be considered expired.
     *   - If null is passed, a default value MAY be used. If none is set,
     *     the value should be stored permanently or for as long as the
     *     implementation allows.
     *
     * @throws CacheException
     *   If there was a problem saving the value in the cache.
     */
    public function set($key, $value, $ttl = null);

    /**
     * @param string $key
     *   Key for the value in the cache.
     *
     * @throws CacheException
     *   If there was a problem deleted the value from the cache.
     */
    public function delete($key);

    /**
     * @throws CacheException
     *   If there was a problem clearing the cache.
     */
    public function clear();
}