Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

iOS Object-Oriented Objective-C Memory, Arrays and Loops, Oh My! Alloc and Init

2 questions. Why do the values in initWithObjectsAndKeys come before the keys? Why do we put "nil" at the end?

Wouldn't it make more sense for the key to come first?

variable_assignment.mm
NSMutableDictionary *carDict = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"Honda", @"Make", @"Accord", @"Model", nil];

1 Answer

Anjali Pasupathy
Anjali Pasupathy
28,883 Points

It would probably make more sense to put the key first. I'm guessing the objects are first because the init method is called initWithObjectsAndKeys, which implicitly places the objects first. As for why objects are first in the init method... my guess is that it makes the init method look sort of like the NSArray init method (initWithObjects), perhaps to create some consistency in that regard.

nil is at the end to tell the compiler that this is the end of the NSDictionary. nil is also at the end of the NSArray init method for the same reason.