custom_cache_backend.php

<?php

//a developer wants to create its own cache backend

class MyOwnBackend implements Phalcon\Cache\BackendInterface 
{

    public function __construct($frontendObject, $backendOptions=array()){
    }

    public function get($keyName, $lifetime=null){
    }

    public function save($keyName=null, $content=null, $lifetime=null, $stopBuffer=true){
    }

}

Phalcon_Cache_Backend_Mongo.php

<?php

//this is provided by phalcon

namespace Phalcon\Cache\Backend;

class Mongo extends \Phalcon\Cache\Backend 
#if not RELEASE
implements Phalcon\Cache\BackendInterface 
#endif
{

    public function __construct($frontendObject, $backendOptions=array()){
    }

    public function get($keyName, $lifetime=null){
    }

    public function save($keyName=null, $content=null, $lifetime=null, $stopBuffer=true){
    }

}

Phalcon_Cache_BackendInterface.php

<?php

//this is provided by phalcon

namespace Phalcon\Cache;

interface BackendInteface {

    public function __construct($frontendObject, $backendOptions=array());
    public function get($keyName, $lifetime=null);
    public function save($keyName=null, $content=null, $lifetime=null, $stopBuffer=true);

}