Are there deep reasons to create a collection of funds for storing zero?

Question

Everyone knows that Foundation collections, such as NSArray, NSDictionaryand NSSet, cannot store objects niland you should use them instead NSNull. I’m sure that if I dig into the open source Core Foundation source code, I could even find where it is forced.

I do not understand why they are so designed? Is it simply because it is nilused as a controller in some of its designers, or is there a deeper reason for this behavior?

Answer 1

, . , , Cocoa. , , , ", ". , , , nil, , , . - , . .

, :

• , [dict objectForKey:@"myKey"] nil. , nil @"myKey" , ?
• ( NSArray , -containsObject: -indexOfObject:) -isEqual: . [nil isEqual:anything] false. nil . nil, ) , -isEqual: , b) .
• -lastObject, -firstObject -anyObject nil, . a nil, ? , -[NSEnumerator nextObject].