We can use a pattern called Double Dispatch to pull out the variation into the subclasses in such a way that we don't break existing interface contracts.

我们可以使用称为双重分发的模式将变化推入子类中，通过这种方式，我们不需要破坏现有的接口定义。

youdao

And the question is, can we break out of that pattern?

WHITEHOUSE: President Obama��s Town Hall in Cannon Falls, Minnesota