Question

I need to use non-copyable objects as keys in the NSMutableDictionary which, by default, is not allowed. I understand the reasons for this not being allowed (retaining the key object, unlike the value object, is undesirable), but it seems like in my particular situation there could be a way around this.

The thing is that I’m only need to query the dictionary using the key’s address, i.e. having the lookup predicate

if (providedKey == storedKey)

instead of

if ([providedKey isEqual:storedKey])

would be perfectly sufficient.

Is there a way of extracting the object’s reference address (or other form of identity) as a copyable comparable object which I could use as a dictionary key instead of the object itself?

Answer 1

It seems that +[NSValue valueWithPointer:] might be what you want. It stores the pointer itself in an object that conforms to NSCopying, so that you can use it as a dictionary key. Retrieve the pointer using pointerValue.