Question

Some of Apple’s obj-c API’s still use C functions, e.g.:

-(NSArray * ) sortedArrayUsingFunction: (NSInteger (*)(id, id, void *))comparator
context:(void *)context

…which is great, except I’m struggling to see how you can store fn-pointers inside ObjC classes.

e.g. to share the same “sort” function in different parts of your program. Say you have different data, in different contexts/classes, but you want the same sort in both places (for consistency).

I’m sure this is simple, but either my C is too rusty, or there’s some gotcha. I tried sticking a plain variable inside the header file:

NSInteger (*)(id, id, void *) myComparator;

…and all I get is a compiler error:

Expected identifier or ‘(‘ before ‘)’ token

Answer 1

Instead of doing:

NSInteger (*)(id, id, void *) myComparator;

Use this instead:

NSInteger (* myComparator)(id, id, void *);

(This is just like block syntax, except blocks use ^ instead of *)