### Access Interceptor Value Holder Proxy

An access interceptor value holder is a smart reference proxy that allows you to dynamically define logic to be executed before or after any of the wrapped object's methods logic.

It wraps around a real instance of the object to be proxied, and can be useful for things like:

- caching execution of slow and heavy methods
- log method calls
- debugging
- event triggering
- handling of orthogonal logic, and AOP in general

### Example

Here's an example of how you can create and use an access interceptor value holder:

    <?php

    use ProxyManager\Factory\AccessInterceptorValueHolderFactory as Factory;

    require_once __DIR__ . '/vendor/autoload.php';

    class Foo
    {
        public function doFoo()
        {
            echo "Foo!\n";
        }
    }

    $factory = new Factory();

    $proxy = $factory->createProxy(
        new Foo(),
        array('doFoo' => function () { echo "PreFoo!\n"; }),
        array('doFoo' => function () { echo "PostFoo!\n"; })
    );

    $proxy->doFoo();

This send something like following to your output:

    PreFoo!
    Foo!
    PostFoo!

### Implementing pre- and post- access interceptors

A proxy produced by the `ProxyManager\Factory\AccessInterceptorValueHolderFactory` implements both the `ProxyManager\Proxy\ValueHolderInterface` and the `ProxyManager\Proxy\AccessInterceptorInterface`.

Therefore, you can set an access interceptor callback by calling:

    $proxy->setMethodPrefixInterceptor('methodName', function () { echo 'pre'; });
    $proxy->setMethodSuffixInterceptor('methodName', function () { echo 'post'; });

You can also listen to public properties access by attaching interceptors to `__get`, `__set`, `__isset` and `__unset`.

A prefix interceptor (executed before method logic) should have following signature:

    /**
     * @var object $proxy       the proxy that intercepted the method call
     * @var object $instance    the wrapped instance within the proxy
     * @var string $method      name of the called method
     * @var array  $params      sorted array of parameters passed to the intercepted
     *                          method, indexed by parameter name
     * @var bool   $returnEarly flag to tell the interceptor proxy to return early, returning
     *                          the interceptor's return value instead of executing the method logic
     *
     * @return mixed
     */
    $prefixInterceptor = function ($proxy, $instance, $method, $params, & $returnEarly) {};

A suffix interceptor (executed after method logic) should have following signature:

    /**
     * @var object $proxy       the proxy that intercepted the method call
     * @var object $instance    the wrapped instance within the proxy
     * @var string $method      name of the called method
     * @var array  $params      sorted array of parameters passed to the intercepted
     *                          method, indexed by parameter name
     * @var mixed  $returnValue the return value of the intercepted method
     * @var bool   $returnEarly flag to tell the proxy to return early, returning the interceptor's
     *                          return value instead of the value produced by the method
     *
     * @return mixed
     */
    $suffixInterceptor = function ($proxy, $instance, $method, $params, $returnValue, & $returnEarly) {};

### Tuning performance for production

See Tuning ProxyManager for Production.