C library function - qsort() - Tutorialspoint.
A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function whose type is not compatible with the pointed-to type, the behavior is undefined.The compare argument is a pointer to a function you must supply that takes a pointer to the key argument and to an array element, in that order. The qsort() function calls this function one or more times during the search. The function must compare the key and the element and return one of the following values.The function qsort() sorts the num element of the array pointed by base. Every element has a size of size bytes long. The qsort function will use the comparator function to determine the order of the elements. The function will not return a value. The content is modified in the newly sorted order.
The C standard requires the comparison function to implement a total order on the items in the input array. A qsort function was in place in Version 3 Unix of 1973, but was then an assembler subroutine. A C version, with roughly the interface of the standard C version, was in-place in Version 6 Unix.The disadvantage with doing so is having to rewrite the function for every new comparison strategy. A better implementation would be to write a sorting function that accepts a pointer to the function that compares each pair of strings. Doing this will mean only passing a pointer to the sorting function with every new comparison strategy.
While a classic comparator function can not readily be passed from AppleScript to ObjC, we can at least write a custom function which lifts atomic values into records (with keys to base and derivative values), and also passes a sequence of (key, bool) pairs, where the bool expresses the choice between ascending and descending order for the paired key.
