众所周知，在很多编程语言中，对一个变量递增1用++，递减1用--，在Swift3之前也是可以这么用的，但之后被取消了。
所以在目前Swift5的版本中，只能用+=1和-=1来进行递增和递减了
如果坚持用++或--将会提示以下错误：
Use of unresolved operator '++'; did you mean '+= 1'?
Use of unresolved operator '--'; did you mean '-= 1'?
也是好奇为毛Swift把这么好用的语法取消了，之前也有老外咨询过Chris Lattner（Swift语言缔造者），并获得了回复。 最近也是被学生问起这个问题，所以拿出来分享一下，以下是我总结的：
- 这是Swift的新功能（我就这么弄，怎么了）
++也并没比+= 1简洁多少- 别把Swift和别的语言混淆在一起（这，就是个性）
- 别的语言的
++主要是用在for循环中：for i = 0; i < n; i++ { ... }，但Swift语言的for循环可以这么写：for i in 0..<n { ... }，所以++就没什么用了 ++读起来不太拟人，感觉没什么意义，不符合Swift语言一贯的超长命名方式，比如x - ++x或foo(++x, x++)，没注释的话之后连自己都看不懂。- 作者本人不喜欢
++和--
一句话：我们不一样！
以下是Chris Lattner答复的原文：
1.These operators increase the burden to learn Swift as a first programming language - or any other case where you don't already know these operators from a different language.
2.Their expressive advantage is minimal - x++ is not much shorter than x += 1.
3.Swift already deviates from C in that the =, += and other assignment-like operations returns Void (for a number of reasons). These operators are inconsistent with that model.
4.Swift has powerful features that eliminate many of the common reasons you'd use ++i in a C-style for loop in other languages, so these are relatively infrequently used in well-written Swift code. These features include the for-in loop, ranges, enumerate, map, etc.
5.Code that actually uses the result value of these operators is often confusing and subtle to a reader/maintainer of code. They encourage "overly tricky" code which may be cute, but difficult to understand.
6.While Swift has well defined order of evaluation, any code that depended on it (like foo(++a, a++)) would be undesirable even if it was well-defined.
7.These operators are applicable to relatively few types: integer and floating point scalars, and iterator-like concepts. They do not apply to complex numbers, matrices, etc.
Finally, these fail the metric of "if we didn't already have these, would we add them to Swift 3?"
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