EnterableScope.java

public class EnterableScope implements Scope
{
  private HashMap<Key<?>, Object> values;
 
  public void enter()
  {
    values = new HashMap<Key<?>, Object>();
  }
 
  public void exit()
  {
    values = null;
  }

  @Override
  public <T> Provider<T> scope(final Key<T> key, final Provider<T> unscoped)
  {
    return new Provider<T>() {
      @Override
      @SuppressWarnings("unchecked")
      public T get()
      {
        // if values is null return null otherwise return the stored value of one exists
        Object object = values != null ? values.get(key) : null;
       
        if(object == null)
        {
          object = unscoped.get();
         
          // if we in scope, store it, otherwise always create a new one
          if(values != null)
          {
            values.put(key, object);
          }
        }
        return (T) object;
      }
    };
  }
}