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1·This implements the types so they can be used with the subscript operator.

这实现了使他们可以用下标操作使用的类型。

2·It is crucially important to understand that we may use the subscript operator, (the operator), to fetch only elements that actually exist. For example.

对于下标操作符(操作符)的使用有一点非常重要，就是仅能提取确实已存在的元素，例如。