objective-c - NSArray 对象里存储的元素为什么可以通过“数组下标”进行访问？

Question

NSArray 不是OC里的内置数据类型，只是Cocoa库中的一个常用类。 那么用objectAtIndex方法，通过传入index参数进行访问NSArray里的元素，例如[arr objectAtIndex:5]即调用方法，这是可以理解的。但是arr[5]这种写法，为什么是属于合法的呢？按理说NSArray不是语言层的东西，应该是更高层级的，怎么还能有特殊的方法调用？

Answer 1

This is a new feature of Objective-c LLVM 4.0.

Recommended reference article: http://blog.csdn.net/kindazrael/article/details/8091201

Answer 2

The so-called syntactic sugar makes it more convenient for programmers to write. Almost all mainstream programming languages ​​support such features. It is not a question of whether it is advanced or not. Shouldn’t the more advanced it be, the more trouble it will have? There is no such truth.

Going a step further, is there any difference between objectAtIndex and syntactic sugar? In the end, what the computer sees is 0 and 1, so what else is not syntactic sugar?