Re: Syntactic sugar to access arrays and hashes in Objective-C

[John Holdsworth <mac at johnholdsworth dot com>]

Hi gcc'ers,

I was wondering if it would be a useful extension to Objective-C  
expand the [] operator
to support array and hash references to NSArray and NSDictionary  
classes directly to
greatly improve the readability of code:

NSArray<AVAudioPlayer *> *players = [NSArray arrayWithObjects:..., nil];

[players[0] play]; // expanded by compiler to: [(AVAudioPlayer *) 
[players objectAtIndex:0] play];
players[0] = aPlayer // expanded to: [players replaceObjectAtIndex:0  
withObject:aPlayer]; or for NSDictionary:

NSDictionary<AVAudioPlayer *> *playersDict = [NSDictionary ....];

[playersDict[@"playerOne"] play]; // -> [(AVAudioPlayer *)[playersDict  
objectForKey:@"playerOne"] play];
playersDict[@"playerTwo"] = aPlayer; // becomes: [players  
setObject:aPlayer forKey:@"playerTwo"];

This also makes use of a form of templates for Objective-C containers  
which might also be a useful extension.

@interfcae NSArray<T> : NSObject {
- (T)objectAtIndex:(NSUInteger)index;
@end

@interface NSMutableObject<T> : NSArray {
- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(T)anObject
@end

Where not specified, type T would default to (id) for backward  
compatibility.

I've looked at the code and such an extension would involve code  
generation inside
the subscript operator which looks difficult but if you want me to  
have a go and
can provide some pointers let me know. I know this introduces coupling  
between
the compiler and the runtime but I would have thought the benefits  
outweighed this.

Perhaps classes which wish to support subscripting make methods  
available by convention:

for NSArray:
- (id)operatorSubscriptInt:(NSUInteger)index;
- (id)operatorSubscriptObject:(id)key;

for NSDictionary
- (id)operatorSubscriptInt:(NSUInteger)index setValue:(id)anObject;
- (id)operatorSubscriptObject:(id)key setValue:(id)anObject;

I know, it sounds like one step on the way to operator overloading....

Best Regards & Thanks for your work,

John Holdsworth