Why Doesn't NSArray return NULL for nonexistent indexes?
cocoa, nsarray, objective-c
Solution
Messages to nil is a language level feature, not a framework API feature.
That `NSArray` (and other classes) throw an exception to indicate programmer error is a conscious design decision that was made when the API was designed (~1993). As both Kevin and Richard indicate, `nil eats message` is not erroneous in anyway whereas `out of bounds` is very much a case of erroneous input.
Where would you draw the line? Should `substringWithRange:` accept any old input? How about `setObject:atIndex:`?
By making NSArray @throw on bounds exceptions for `indexOfObject:` it makes the API consistent; any index (or range) that is out of bound will `@throw`.
Problem
The way I understand it one of the things special about Objective C is that you can send messages to NULL and it will just ignore them instead of crashing. Why is it that NSArray doesn't just return a NULL object if the index requested is out of bounds instead of causing a NSRangeException? What I would expect from Objective C and NSArray is the following. ``` NSArray *array = [NSArray arrayWithObjects:@"Object 1", @"Object 2", @"Object 3", nil]; for (int i = 0; i < 5; i++) { NSString *string = [array objectAtIndex:i]; if (string) { NSLog(@"Object: %@",string); } } ``` Allowing me to access indexes of the array with don't contain objects and simply returning NULL. Then I can check if the object exists. I can do this in other places such as checking if the object has been instantiated. ``` NSArray *array; if (!array) { array = [NSArray array]; } ``` I realize this is a theory based question but I'm curious :)