"Rolodex"是一种普通索引系统的商标名称,通常被繁忙的管理人员所使用。
"Rolodex" is the commercial name of a common in-dex system much used by busy executives.
如果使用普通索引的话，即使你并不打算对它进行查询，它也会因为null值浪费大量的空间。
While a normal index can be used, it wastes a lot of space for nulls you are probably not going to query against.
普通数组的元素用整数作为索引，而关联数组的元素用名称作为索引，而不是整数。
The elements of ordinary arrays are indexed by integers, whereas the elements of associative arrays are indexed by names instead of Numbers.
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