swift语言的特点（相对于oc）

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

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上述为swift最大的特点

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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.

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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.