Question

Is it possible to access NSArray’s objects using [idx]? I have a standard library that uses [] style indexing and I don’t want to rewrite the whole library to suit ObjC’s objectAtIndex: method.

As in, NSArray *obj = [NSArray ...]; id item = obj[0];

Answer 1

The accepted answer (whilst true at the time) is now out of date. As of Xcode 4.5, you can now set and get NSArray elements using:

id object = array[5]; // equivalent to [array objectAtIndex:5];
mutableArray[5] = object; // equivalent to [mutableArray replaceObjectAtIndex:5 withObject:object];

You can also do the same for NSDictionaries using:

id object = dict[@"key"]; // equivalent to [dict objectForKey:@"key"];
mutableDict[@"key"] = object; // equivalent to [mutableDict setObject:object forKey:@"key"];

Even cooler, you can now create array and dictionary objects using JSON-like syntax:

NSArray *array = @[@"value1", @"value2"]; // equivalent to [NSArray arrayWithObjects:@"value1", @"value2", nil];
NSDictionary *dict = @{@"key1":@"value1", @"key2":@"value2"}; // equivalent to [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];

And in a similar vein, boxed values like NSNumber can now be written in a shorthand syntax:

NSNumber *intNumber = @5; // equivalent to [NSNumber numberWithInteger:5];
NSNumber *boolNumber = @YES; // equivalent to [NSNumber numberWithBool:YES];
NSNumber *someNumber = @(variable); // equivalent to [NSNumber numberWithWhatever:variable];

EDIT:

Far more detailed answer than mine here: What are the details of "Objective-C Literals" mentioned in the Xcode 4.4 release notes?

EDIT 2:

To be clear, though this feature wasn’t added until Xcode 4.5, it works on iOS 4.3 and above, so you don’t have to avoid using this if you need to support older iOS versions.

EDIT 3:

For the sake of pedantic precision, it works on Apple LLVM compiler version 4.1 and above. AKA the version that shipped with Xcode 4.5.