在swift中，似乎有两个相等运算符：double equals(==)和triple equals(===)，两者之间有什么区别？
！==和===是身份运算符，用于确定两个对象是否具有相同的引用。
Swift also provides two identity operators (=== and !==),which you use to test whether two object references both refer to the same object instance.
摘录自：Apple Inc.“Swift编程语言”iBooks。 https://itun.es/us/jEUH0.l
