Performance of NSDictionary initialization

TestDictionaryPerformance.m

- (void)test_stepByStep_withCapacity
{
    NSMutableArray *keys = [NSMutableArray new];
    NSMutableArray *values = [NSMutableArray new];
    srand(0x21112005);
    int entryCount = 1000000;
    for (int ix = 0, ixMax = entryCount; ix < ixMax ; ix++) {
        NSString *key = [NSString stringWithFormat:@"Key#%d", (ix + 1)];
        NSString *value = [NSString stringWithFormat:@"Value with %d", rand()];
        [keys addObject:key];
        [values addObject:value];
    }
    
    // Step-by-step with initial capacity (0.411 sec)
    [self measureBlock:^{
        NSMutableDictionary *stepByStep = [NSMutableDictionary dictionaryWithCapacity:entryCount];
        [keys enumerateObjectsUsingBlock:^(NSString * _Nonnull key, NSUInteger idx, BOOL * _Nonnull stop) {
            stepByStep[key] = values[idx];
        }];
        IfoDebug(@"Dictionary has %d entries", stepByStep.count);
    }];
}

- (void)test_stepByStep_noInitialCapacity
{
    NSMutableArray *keys = [NSMutableArray new];
    NSMutableArray *values = [NSMutableArray new];
    srand(0x21112005);
    int entryCount = 1000000;
    for (int ix = 0, ixMax = entryCount; ix < ixMax ; ix++) {
        NSString *key = [NSString stringWithFormat:@"Key#%d", (ix + 1)];
        NSString *value = [NSString stringWithFormat:@"Value with %d", rand()];
        [keys addObject:key];
        [values addObject:value];
    }
    
    // Step-by-step without initial capacity (0.788 sec)
    [self measureBlock:^{
        NSMutableDictionary *stepByStep = [NSMutableDictionary new];
        [keys enumerateObjectsUsingBlock:^(NSString * _Nonnull key, NSUInteger idx, BOOL * _Nonnull stop) {
            stepByStep[key] = values[idx];
        }];
        IfoDebug(@"Dictionary has %d entries", stepByStep.count);
    }];
}

- (void)test_atOnce
{
    NSMutableArray *keys = [NSMutableArray new];
    NSMutableArray *values = [NSMutableArray new];
    srand(0x21112005);
    int entryCount = 1000000;
    for (int ix = 0, ixMax = entryCount; ix < ixMax ; ix++) {
        NSString *key = [NSString stringWithFormat:@"Key#%d", (ix + 1)];
        NSString *value = [NSString stringWithFormat:@"Value with %d", rand()];
        [keys addObject:key];
        [values addObject:value];
    }
    
    // At once (0.271 sec)
    [self measureBlock:^{
        NSDictionary *atOnce = [NSDictionary dictionaryWithObjects:values forKeys:keys];
        IfoDebug(@"Dictionary has %d entries", atOnce.count);
    }];
}