My Wish: Syntax Additions to Objective-C for Object Literals

I have written before about the preference for clarity over brevity in the Objective-C/Cocoa world that leads to extraordinarily long method signatures. While I like the expressiveness of this approach, there are occasions where I feel the language could be more concise without giving up anything. Most of the time, this has to do with often-used objects like NSNumber, NSArray, and NSDictionary. I wish Objective-C included a syntax to quickly define object literals of these types as we can already do with strings.

Objective-C has understood the syntax @"Some string" to define a literal string object for a long time (not since the beginning, though: the @"..." was not part of the original implementation of Objective-C). So why not define a similar syntax for other object literals? Here are some I would love to see in a future version of the language:

New syntax Equivalent to
@1 [NSNumber numberWithInteger:1]
@2.5f [NSNumber numberWithFloat:2.5f]
@2.5 [NSNumber numberWithDouble:2.5]
@YES [NSNumber numberWithBool:YES]
@[@"abc", @1, @2.5, @NO] [NSArray arrayWithObjects:@"abc", [NSNumber numberWithInteger:1], [NSNumber numberWithDouble:2.5], [NSNumber numberWithBool:NO], nil]
@{ @"name": @"John Appleseed", @"age": @38 } [NSDictionary dictionaryWithObjectsAndKeys: @"John Appleseed", @"name", [NSNumber numberWithInteger:38], @"age", nil]

As an example of how such syntax additions could influence the look of your code, consider the creation of a keyframe animation. Currently:

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"alpha"];
animation.values   = [NSArray arrayWithObjects:
                      [NSNumber numberWithFloat:1.0f],
                      [NSNumber numberWithFloat:0.8f],
                      [NSNumber numberWithFloat:0.0f],
animation.keyTimes = [NSArray arrayWithObjects:
                      [NSNumber numberWithFloat:0.0f],
                      [NSNumber numberWithFloat:0.6f],
                      [NSNumber numberWithFloat:1.0f],
[self.view.layer addAnimation:animation forKey:@"alpha"];

With the new syntax, this could be written in a much clearer way in my opinion:

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"alpha"];
animation.values   = @[@1.0f, @0.8f, @0.0f];
animation.keyTimes = @[@0.0f, @0.6f, @1.0f];
[self.view.layer addAnimation:animation forKey:@"alpha"];

Update January 14, 2011: Comments from readers:

Jens Ayton:

allow the @ to be dropped inside compound literals, since you can’t put primitives there anyway. Also, allow keyword-like dictionary keys to be unquoted, as in JavaScript.

Bavarious points to a set of macros Mike Ash has created to simplify the making of collections: MACollectionUtilities. The syntax isn’t as nice, but they are easy to implement.

My coworkers Christian and Alexis suggest two more literals:

  • @/…/ for NSRegularExpression
  • @<> for NSData with binary content (in hex)

Update May 10, 2012: Stig Brautaset pointed out to me that he already wrote about this topic in 2008 and made very similar suggestions. Thanks Stig, I didn’t know!