php - Doctrine AnnotationDriver Excepted AnnotationReader,but could use CachedReader -

when use cachedreader doctrine 2.5 annotationdriver this:

$reader = new cachedreader(new annotationreader(), $cachedriver,false); $driverimpl = new annotationdriver($reader,$modelpath); 

i got tip ide: excepted annotationreader, give cachedreader.

i check annotationdriver source code , shows annotataiondriver constructor(extends abstract class) need annotationreader.

i know both of annotationreader , cachedreader implements reader interface.

why not annotationdriver need interface of reader annotationreader class?