Initial model to for Memcache connection

CacheModel.php

<?php
namespace App/Models;

class CacheModel
{

    private $instance = null;

    public function __construct()
    {
        if (! class_exists('Memcached'))
        {
            throw new \Exception('Memcached class does not exist');
        }
        
        $persistent_id  = defined('APP_NAME') ? APP_NAME : 'memcache_connection';
        $this->instance = (new Memcached($persistent_id))->addServer('localhost', '11211');
    }

    /**
     * function to set key in memcache
     * @param $key
     * @param $value
     * @param $expiry optional
     */
    public function set($key, $value, $expiry = null)
    {
        if (! $this->instance)
            return false;

        if ($expiry)
            return $this->instance->set($key, $value, $expiry);
		
        return $this->instance->set($key, $value);
    }

    /**
     * function to get key from memcache
     * @param $key
     */
    public function get($key)
    {
        if (! $this->instance)
            return false;

        return $this->instance->get($key) ?? false;
    }

    /**
     * function to delete a key from memcache
     * @param $key
     */
    public function delete($key)
    {
        if (! $this->instance)
            return false;

        $this->instance->delete($key);
    }

    /**
     * function to delete all keys from memcache
     */
    public function flush()
    {
        if (! $this->instance)
            return false;

        $this->instance->flush();
    }
}