(PHP 5 >= 5.2.0, PHP 7)
ArrayIterator::uksort — Sort by keys using a user-defined comparison function
This method sorts the elements by keys using a user-supplied comparison function.
Note:
If two members compare as equal, their relative order in the sorted array is undefined.
cmp_function在第一个参数小于，等于或大于第二个参数时，该比较函数必须相应地返回一个小于，等于或大于 0 的整数。
没有返回值。