So when the program starts to loop through the files, perhaps to determine the directories overall size, it has to requery the file system one by one.
所以，在程序开始遍历这些文件的时候，假设为了确定目录的总大小，就必须逐一重新查询文件系统。
Simplicity: the program can use these node tests to select a group of elements based on their common group head element or type definition rather than enumerate all concrete element names one by one.
简单性：程序可以使用这些节点测试，选择基于共同组head元素或类型定义的一组元素，而不是逐一列举所有具体的元素名。
It is more efficient to calculate this iterator directly than to write an equivalent program that increments the iterator one by one until it reaches the middle element.
这种直接计算迭代器的方法，与用迭代器逐个元素自增操作到达中间元素的方法是等价的，但前者的效率要高得多。
It is more efficient to calculate this iterator directly than to write an equivalent program that increments the iterator one by one until it reaches the middle element.
这种直接计算迭代器的方法，与用迭代器逐个元素自增操作到达中间元素的方法是等价的，但前者的效率要高得多。
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