swift学习笔记1 操作符
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注:英文部分来自官方文档
基础操作符
赋值操作符
If the right side of the assignment is a tuple with multiple values, its elements can be decomposed into multiple constants or variables at once:
如果赋值的左边是一个包含多个值的tuple,它的元素可以一次解析为多个常量或变量
let (x, y) = (1, 2)// x 等于 1, y等于 2
Unlike the assignment operator in C and Objective-C, the assignment operator in Swift does not itself return a value. The following statement is not valid:
和c oc中的赋值操作符不一样,swift中的赋值操作赋本身并不返回一个值。下面的程序是无效的:
if x = y { //无效, x = y 并不返回值.}
nil聚合运算符 Nil-Coalescing
The nil-coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that is stored inside a.
nil聚合运算符(a ?? b) 表示:如果a包含一个值,则解析可选a;如果a为nil,则返回默认值b。 此表达式是一个可选(optional)类型。表达式b必须与a内部存储的类型一致。
The nil-coalescing operator is shorthand for the code below:
nil聚合运算符 是下面代码的简写:
a != nil ? a! : b
范围操作符 Range Operators
- 闭合范围操作符 Closed Range Operator
The closed range operator (a…b) defines a range that runs from a to b, and includes the values a and b. The value of a must not be greater than b.
闭合范围操作符 (a…b) 定义了一个 从a到b的范围(注意中间是三点),而且包含值a和b。a的值必须必b的值大。
闭合操作符在for-in循环中特别有用:
for index in 1...5 { print("\(index) times 5 is \(index * 5)")}// 1 times 5 is 5// 2 times 5 is 10// 3 times 5 is 15// 4 times 5 is 20// 5 times 5 is 25
- 半开范围操作符 Half-Open Range Operator
The half-open range operator (a..
let names = ["Anna", "Alex", "Brian", "Jack"]let count = names.countfor i in 0..<count { print("Person \(i + 1) is called \(names[i])")}// Person 1 is called Anna// Person 2 is called Alex// Person 3 is called Brian// Person 4 is called Jack
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