enumerateObjectsUsingBlock，for in,for的区别和性能测试

一、

1.for in 比for高效.

2.enumerateObjectsUsingBlock和for in 效率差不多，enumerateObjectsUsingBlock有时候会比for in 快.

3.enumerateObjectsUsingBlock要修改局部变量的时候，局部变量要声明成__block类型.

4.CFAbsoluteTimeGetCurrent 获取当前时间,多用于函数的性能测试.

二、

- (void)enumerateObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void
(^)(ObjectType obj, NSUInteger idx,BOOL *stop))block
其中opts包含两种类型：

 NSEnumerationConcurrent = (1UL <<0),//并发，顺序不确定

   
 NSEnumerationReverse = (1UL <<1),//倒叙，顺序确定

NSArray版

- (void)enumerateObjectsUsingBlock:(void (^)(ObjectType obj,NSUInteger
idx, BOOL *stop))block 

- (void)enumerateObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void
(^)(ObjectType obj, NSUInteger idx,BOOL *stop))block

- (void)enumerateObjectsAtIndexes:(NSIndexSet *)s options:(NSEnumerationOptions)opts
usingBlock:(void (^)(ObjectType obj,NSUInteger idx,BOOL *stop))block 

NSDictionary版

- (void)enumerateKeysAndObjectsUsingBlock:(void (^)(KeyType key, ObjectType obj,BOOL
*stop))block 

- (void)enumerateKeysAndObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void
(^)(KeyType key, ObjectType obj, BOOL *stop))block 
字典版的可以同时取key和value(forin只能取key再手动取value),如：

 NSDictionary *dict =@{@"one":@"Lily",@"tow":@"LiLei",@"three":@"Lucy"};

    [dict enumerateKeysAndObjectsUsingBlock:^(id _Nonnull key,id _Nonnull
obj,BOOL *_Nonnull stop) {

        NSLog(@"key%@,value%@",key,obj);

    }];

References：
http://www.cocoachina.com/industry/20140531/8630.html http://www.cnblogs.com/skyming/p/3977075.html