Cache.php

<?php

interface Cache
{
    public function get($id);
    public function set($id, $value);
}

EagerCache.php

<?php

class EagerCache implements Cache
{
    private $values = array();
    private $storage;
    private $storageId;
    private $isDirty = false;
    
    public function __construct(Backend $storage, $storageId)
    {
        $this->storage = $storage;
        $this->storageId = $storageId;
        $content = $storage->doFetch($storageId);
        if (is_array($content)) {
            $this->values = $content;
        }
    }
    
    public function get($id)
    {
        return $this->values[$id];
    }
    
    public function set($id, $value)
    {
        $this->values[$id] = $value;
    }
    
    // or could be done with a TerminableCache like Symfony's Terminable kernel
    public function __destruct()
    {
        if ($this->isDirty) {
            $this->storage->doSave($this->storageId, $this->content, $ttl);
        }
    }
}

TransientCache.php

<?php

class TransientCache implements Cache
{
    private $values = array();
    
    public function get($id)
    {
        return $this->values[$id];
    }
    
    public function set($id, $value)
    {
        $this->values[$id] = $value;
    }
}

TtlCache.php

<?php

class TtlCache implements Cache
{
    private $ttl;
    private $backend;
    
    public function __construct(Backend $backend, $ttl)
    {
        $this->backend = $backend;
        $this->ttl = $ttl;
    }
    
    public function get($id)
    {
        return $this->backend->get($id, $ttl);
    }
    
    public function set($id, $value)
    {
        $this->backend->set($id, $value, $ttl)
    }
}