类型安全

Swift是一种类型安全的语言.类型安全语言鼓励您清楚代码可以使用的值的类型.如果您的部分代码需要String,则不能错误地将其传递给Int.

var welcomeMessage: String
welcomeMessage = 22 // this would create an error because you  
//already specified that it's going to be a String

类型推断

如果未指定所需的值类型,Swift将使用类型推断来计算出适当的类型.类型推断使编译器能够在编译代码时自动推断出特定表达式的类型,只需检查您提供的值即可.

var meaningOfLife = 42 // meaningOfLife is inferred to be of type Int
meaningOfLife = 55 // it Works,because 55 is an Int

类型安全&一起输入推理

var meaningOfLife = 42 // 'Type inference' happened here,we didn't specify that this an Int,the compiler itself found out.
meaningOfLife = 55 // it Works,because 55 is an Int
meaningOfLife = "SomeString" // Because of 'Type Safety' ability you will get an 
//error message: 'cannot assign value of type 'String' to type 'Int''

专家提示：

代码必须进行的类型推断越少,编译速度就越快.因此,建议避免收集文字.收集的时间越长,其类型推断变得越慢……

不错

let names = ["John","Ali","Jane"," Taika"]

好

let names : [String] = ["John"," Taika"]

有关更多信息,请参阅John Sundell的this post.查看“收集文字”部分