On Jan 11, 2016, at 10:18 AM, Dave <d...@looktowindward.com> wrote: > It’s actually an NSInteger so it’s 64 bits isn’t it? But I take your point, > the hash isn’t going to change. > > Any one have any other techniques for telling if a CFTypeRef has changed?
Does CFEqual() do what you need? It depends a lot on what you mean by "has changed". If you have an immutable array containing a mutable object, do you want to detect that? If you have a CFFileDescriptorRef, do you care about the whole contents and metadata of the file, etc.? >> FYI, since hash functions can be tricky, a useful technique I use to reason >> about them is to imagine a deliberately stupid hash function. For instance, >> imagine that the hash function for strings simply returns the first 4 bytes >> of the string. (Yes, this meets the criteria for a correct hash function, >> it’s just going to be inefficient in use.) Amusingly, -[NSString hash] used to depend only on the first four bytes and the length of the string. It was inefficient in use, especially if you were hashing a lot of strings that all started with "http". :) _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
