详解Objective-C中的语法糖@{}究竟是什么

NSMutableDictionary *mDic1 = [NSMutableDictionary dictionaryWithDictionary:@{@"a":@1, @"a":@2}];
//'a': 1
NSMutableDictionary *mDic2 = [NSMutableDictionary dictionary];
[mDic2 setObject:@(1) forKey:@"a"];
[mDic2 setObject:@(2) forKey:@"a"];
 //'a': 2

@{@"a":@1, @"a":@2}

NSDictionary *dic = @{@"a":@1, @"a":@2};
NSLog(@"%@", dic);

- (id)initWithObjects:(const id [])objects forKeys:(const id <NSCopying> [])keys count:(NSUInteger)cnt

+ (id)xxx_dictionaryWithObjects:(const id [])objects forKeys:(const id <NSCopying> [])keys count:(NSUInteger)cnt{
 for (NSUInteger i = 0; i < cnt; i++) {
 id key = keys[i];
 id obj = objects[i];
 NSLog(@"key = %@", key);
 NSLog(@"obj = %@", obj);
 }
 return [[NSDictionary class] xxx_dictionaryWithObjects:objects forKeys:keys count:cnt];
}

+ (id)dictionaryWithDictionary:(NSDictionary *)dict
{
 size_t count = [dict count];
 id *objects = NULL;
 id *keys = NULL;

 if (count > 0) {
 objects = malloc(sizeof(id) * count);
 if (UNLIKELY(objects == NULL)) {
  return NULL;
 }
 keys = malloc(sizeof(id) * count);
 if (UNLIKELY(keys == NULL)) {
  free(objects);
  return NULL;
 }
 }
 
 [dict getObjects:objects andKeys:keys];
 id obj = [[self alloc] initWithObjects:objects forKeys:keys count:count];

 if (objects != NULL) {
 free(objects);
 }
 if (keys != NULL) {
 free(keys);
 }

 return [obj autorelease];
}

 [dict getObjects:objects andKeys:keys];
//或者
 id obj = [[self alloc] initWithObjects:objects forKeys:keys count:count];

CF_PRIVATE Boolean CFBasicHashAddValue(CFBasicHashRef ht, uintptr_t stack_key, uintptr_t stack_value) {
 ···
 CFBasicHashBucket bkt = __CFBasicHashFindBucket(ht, stack_key);
 if (0 < bkt.count) {
  ht->bits.mutations++;
  if (ht->bits.counts_offset && bkt.count < LONG_MAX) { // if not yet as large as a CFIndex can be... otherwise clamp and do nothing
   __CFBasicHashIncSlotCount(ht, bkt.idx);
   return true;
  }
 } else {
  __CFBasicHashAddValue(ht, bkt.idx, stack_key, stack_value);
  return true;
 }
 return false;
}

CF_PRIVATE void CFBasicHashSetValue(CFBasicHashRef ht, uintptr_t stack_key, uintptr_t stack_value) {
 ···
 CFBasicHashBucket bkt = __CFBasicHashFindBucket(ht, stack_key);
 if (0 < bkt.count) {
  __CFBasicHashReplaceValue(ht, bkt.idx, stack_key, stack_value);
 } else {
  __CFBasicHashAddValue(ht, bkt.idx, stack_key, stack_value);
 }
}

[NSDictionary dictionaryWithObjects:@[@1,@2,@3,@4,@5,@6,@7,@8,@9,@0] forKeys:@[@"a",@"b", @"a", @"b", @"a", @"a", @"b", @"b", @"a", @"b"]]