package cache;
public abstract aspect Caching {
  public interface Cached {
    java.util.Vector allInvalidated();
  }
  Object Cached.cachedValue; 
  void Cached.clearCache() {
    System.err.println("cache cleared"); 
    cachedValue = null;
  }
  public abstract pointcut cache(Cached t);
  public abstract pointcut invalidate(Cached t);
  Object around(Cached t): cache(t) {  /* \label{line:cache1} */
    if(t.cachedValue==null) {
      t.cachedValue = proceed(t);      /* \label{line:cache2} */
      System.err.println("value cached: " + t.cachedValue); 
    } else {
      System.err.println("cache hit " + t.cachedValue); 
    }
    return t.cachedValue;
  }
  before(Cached t):invalidate(t) {
    java.util.Iterator it = t.allInvalidated().iterator();
    while (it.hasNext()) 
      ((Cached)it.next()).clearCache();
  }
}