Lets see if we can kickstart this blog with a quickie Cocoa tip. You know it's a bad sign that I always have to look up Markdown syntax every time I post because I've forgotten since the last time.

In Snow Leopard, Apple added some enumeration methods to several collection classes that use blocks. Several of those use a mysterious NSEnumerationOptions parameter. There aren't any links in the docs to the valid flag values for NSEnumerationOptions parameters.

NSArray: -enumerateObjectsWithOptions:usingBlock:, -enumerateObjectsAtIndexes:options:usingBlock:
NSDictionary: -enumerateKeysAndObjectsWithOptions:usingBlock:
NSSet: -enumerateObjectsWithOptions:usingBlock:
NSIndexSet: -enumerateIndexesWithOptions:usingBlock:, -enumerateIndexesInRange:options:usingBlock:

For anyone else Googling for some answers, I did eventual dig up the documentation for the values.

NSEnumerationConcurrent: invoke the Block on the selected elements concurrently; the order of invocation is nondeterministic and undefined; this flag is a hint and may be ignored by the implementation under some circumstances; the code of the Block must be safe against concurrent invocation

NSEnumerationReverse: invoke the Block on the selected elements in reverse of the natural order; available for NSArrays and NSIndexSets; undefined for NSDictionarys and NSSets, or when combined with the NSEnumerationConcurrent flag

Now, I'll go log a RADAR bug about the missing link...