1.Constants and Variables(常量和变量)
let
定义常量,var
定义变量。
[Note] If a stored value in your code won’t change, always declare it as a constant with the
let
keyword. Use variables only for storing values that need to be able to change.
如果代码中的存储值不会更改,则始终使用let关键字将其声明为常量。仅将变量用于存储需要更改的值。
2.Type Annotations(类型注解)——不同与C语言
Write a type annotation by placing a colon(冒号) after the constant or variable name, followed by a space, followed by the name of the type to use.var/let <变量名>(:)(空格)<类型名>
var welcomeMessage: String
welcomeMessage = "Hello"
The colon in the declaration means “…of type…,” so the code above can be read as:
“Declare a variable called welcomeMessage that is of type String.”
You can define multiple related variables of the same type on a single line, separated by commas, with a single type annotation after the final variable name:
var red, green, blue: Double
[Note]在实践中很少需要编写类型注释。如果在定义常量或变量时为其提供一个初始值,Swift几乎总是可以推断出该常量或变量所使用的类型,如类型安全性和类型推断中所述。在上面的welcomeMessage示例中,没有提供初始值,因此welcomeMessage变量的类型是用类型注释指定的,而不是从初始值推断出来的。
3.Naming Constants and Variables(命名常量和变量)
Constant and variable names can contain almost any character, including Unicode characters:
let π = 3.14159
let 你好 = "你好世界"
let原文地址:https://www.cnblogs.com/lvhang/p/12295942.html
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