1、泛型、泛型约束与扩展；
2、函数式编程；
3、值类型、引用类型；
4、枚举、关联值、元组等其他
上述为swift最大的特点
Another safety feature is that by default Swift objects can never be nil, and trying to make or use a nil object will results in a compile-time error.
Swift is a type-safe language, which means the language helps you to be clear about the types of values your code can work with. If part of your code requires a String, type safety prevents you from passing it an Int by mistake. Likewise, type safety prevents you from accidentally passing an optional String to a piece of code that requires a nonoptional String. Type safety helps you catch and fix errors as early as possible in the development process.