For example, an immutable CFString can store the length and the character data in the same block of memory. And, more generally, there is NSAllocateObject(), which lets you specify extra bytes to be allocated after the object’s ivars. The amount of storage is determined by the particular instance rather than being fixed by the class. This reduces memory use (one allocation instead of two) and improves locality of reference. Is there a way to do this with Swift?
Asked
Active
Viewed 81 times
2
-
Great question. I recently wanted to implement a fixed length array type. This would be really helpful to have. – Nikolai Ruhe Jan 08 '16 at 18:42
1 Answers
0
A rather later reply. NSAllocateObject() is now deprecated for some reason. However, NSAllocateObject() is really a wrapper around class_createInstance which is not deprecated. So, in principle, one could use this to allocate extra bytes for an object instance.
I can't see why this wouldn't work in Swift. But accessing the extra storage would be messy because you'd have to start fooling around with unsafe pointers and the like. Moreover, if you're not the author of the original class, then you risk conflicting with Apple's ivars, especially in cases where you might be dealing with a class cluster which could potentially have a number of different instance sizes, according to the specific concrete implementation.
I think a safter approach would be to make use of objc_setAssociatedObject and objc_getAssociatedObject, which are accessible in Swift. E.g. Is there a way to set associated objects in Swift?
Dave Jewell
- 190
- 1
- 7