A hash index is often implemented using an array where each element in the array is a hash bucket with a fixed size, as is depicted in Figure 1.

hash索引常常使用一个数组来实现，数组中的每个元素是一个有固定大小的hash bucket，如图1所示。

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This speedup is due to the fact that the array is a fixed size, not a variable-sized one like the default PHP one is, and that non-numeric indexes are not allowed.

造成这种速度优势的原因是数组是固定大小的，而默认的 PHP 数组是可变大小的，并且不允许非数值型索引。

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Another useful addition is the SplFixedArray class, which, as the name implies, is a fixed-size array implementation.

另一个有用的补充是splfixedarray类，顾名思义，这是一个固定大小的数组实现。

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