Objective-C Literals: Object Subscripting (LLVM 4.0) - ready to use in iOS 5 & 4!

main.m

// example

int main(int argc, char *argv[])
{
    @autoreleasepool {
        NSMutableArray *array = [NSMutableArray arrayWithObject: @"vorher"];
        NSLog(@"%@", array[0]);
        array[0] = @"haha";
        NSLog(@"%@", array[0]);
        
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        dict[@"test"] = @"jap";
        NSLog(@"%@", dict[@"test"]);
        dict[@"test"] = @"change";
        NSLog(@"%@", dict[@"test"]);
    }
}

NSContainer+Subscripting.h

//
//  NSContainer+Subscripting.h
//
//  Created by Markus Emrich on 10.08.12.
//  Copyright 2012 nxtbgthng. All rights reserved.
//

#if !defined(__IPHONE_6_0) || __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0

#import "NSContainer+Subscripting.h"

@interface NSArray (Subscripting)
- (id)objectAtIndexedSubscript:(NSInteger)index;
@end

@interface NSMutableArray (MutableSubscripting)
- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index;
@end

@interface NSDictionary (Subscripting)
- (id)objectForKeyedSubscript:(id)key;
@end

@interface NSMutableDictionary (MutableSubscripting)
- (void)setObject:(id)object forKeyedSubscript:(id)key;
@end

#endif

NSContainer+Subscripting.m

//
//  NSContainer+Subscripting.m
//
//  Created by Markus Emrich on 10.08.12.
//  Copyright 2012 nxtbgthng. All rights reserved.
//

#if !defined(__IPHONE_6_0) || __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0

#import "NSContainer+Subscripting.h"

@implementation NSArray (Subscripting)
- (id)objectAtIndexedSubscript:(NSInteger)index {
    return [self objectAtIndex:index];
}
@end

@implementation NSMutableArray (MutableSubscripting)
- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index {
    [self insertObject:anObject atIndex:index];
}
@end

@implementation NSDictionary (Subscripting)
-(id)objectForKeyedSubscript:(id)key {
    return [self objectForKey: key];
}
@end

@implementation NSMutableDictionary (MutableSubscripting)
- (void)setObject:(id)object forKeyedSubscript:(id)key {
    [self setObject:object forKey: key];
}
@end

#endif

- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index {
    [self insertObject:anObject atIndex:index];
}

is incorrect. It should use replaceObjectAtIndex:withObject in cases where the index refers to an existing element.