for VS for(... in ...)
NSMutableArray *test = [NSMutableArray array]; for (int i= 0; i < 10000000; i++) { [test addObject:@(i)]; } int sum = 0; double date_s = CFAbsoluteTimeGetCurrent(); for (int i = 0;i < test.count; i++) { sum += 1; } double date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"ForLoop Time: %f", date_e - date_s); date_s = CFAbsoluteTimeGetCurrent(); for (id obj in test) { sum += 1; } date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"Enumeration Time: %f", date_e - date_s); NSMutableArray *test = [NSMutableArray array]; for (int i= 0; i < 10000000; i++) { [test addObject:@(i)]; } int sum = 0; double date_s = CFAbsoluteTimeGetCurrent(); for (int i = 0;i < test.count; i++) { int key = [test[i] intValue]; sum += key; sum -= key; } double date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"ForLoop Time: %f", date_e - date_s); date_s = CFAbsoluteTimeGetCurrent(); for (id obj in test) { int key = [obj intValue]; sum += key; sum -= key; } date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"Enumeration Time: %f", date_e - date_s);enumerateObjectsUsingBlock VS for(... in ...)
for(... in ...)用起来非常方便、简洁，同时 enumerateObjectsUsingBlock: 也有很多新特性:
通常enumerateObjectsUsingBlock: 和 (for(... in ...)在效率上基本一致，有时会快些。主要是因为它们都是基于 NSFastEnumeration 实现的. 快速迭代在处理的过程中需要多一次转换，当然也会消耗掉一些时间. 基于Block的迭代可以达到本机存储一样快的遍历集合. 对于字典同样适用，而数组的迭代却不行。
注意"enumerateObjectsUsingBlock" 修改局部变量时， 你需要声明局部变量为 __block 类型.
enumerateObjectsWithOptions:usingBlock: 支持并发迭代或反向迭代，并发迭代时效率也非常高.
对于字典而言, enumerateObjectsWithOptions:usingBlock 也是唯一的方式可以并发实现恢复Key-Value值.
就个人而言, 我偏向于使用 enumerateObjectsUsingBlock: 当然最后还是要根据实际情况上下文决定用什么
NSMutableArray *test = [NSMutableArray array]; for (int i= 0; i < 10000; i++) { [test addObject:@(i)]; } double date_s = CFAbsoluteTimeGetCurrent(); for (id obj in test) { NSLog(@"%@",obj); } double date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"ForLoop Time: %f", date_e - date_s); date_s = CFAbsoluteTimeGetCurrent();// [test enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {// NSLog(@"%@",obj);// }]; [test enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id obj, NSUInteger idx, BOOL *stop) { NSLog(@"%@",obj);; }]; date_e = CFAbsoluteTimeGetCurrent(); NSLog(@"Enumeration Time: %f", date_e - date_s);
