因为一个给定类型的所有元素不需要有相同的值，所以未知的或者不适用的信息也就不存在了。
Since all the elements of a given type need not have the same structure, information that is unknown or inapplicable can simply not appear.
因为一个给定类型的所有元素不需要有相同的值，所以未知的或者不适用的信息也就不存在了。
Since all the elements of a given type need not have the same structure, information that is unknown or inapplicable can simply not appear.
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