本文是学习《The Swift Programming Language》整理的相关随笔，基本的语法不作介绍，主要介绍Swift中的一些特性或者与OC差异点。
系列文章：
Basic Operators
等号操作符(Assignment Operator)
Unlike the assignment operator in C and
Objective-C, the assignment operator in
Swift does not itself return a value.
- Swift 中的等号操作符，是不会有返回值的；为了避免以下例子中的错误用法(安全性的体现点)。
例子：
var color1 = "red"
var color2 = "green";
if color2 = color1 {
}
编译报错：
error: MyPlayground.playground:50:11:
error: use of '=' in a boolean context, did
you mean '=='?
if color2 = color1 {
~~~~~~ ^ ~~~~~~
==
比较操作符(Comparison Operators)
Swift also provides two identity operators
(=== and !==), which you use to test
whether two object references both refer to
the same object instance. For more
information, see Classes and Structures.
- Swift中引入的
===,!==只能用来比较引用数据类型
例子1：
var color1 = NSString(string: "red");
var color2 = color1;
if color2 === color1{
print("Equal");
}
执行结果：
Equal
例子2：
var color1 = "red";
var color2 = color1;
if color2 === color1{
print("Equal");
}
执行结果:
error: MyPlayground.playground:50:11: error: binary
operator '===' cannot be applied to two 'String' operands
if color2 === color1{
~~~~~~ ^ ~~~~~~
同时得出另一个结论：NSString是引用类型,String是值类型。
等号合并操作符(Nil-Coalescing Operator)
The nil-coalescing operator is shorthand for the code
below: a != nil ? a! : b
例子：
let num1 = 1;
var num2:Int?;
var num3 = num2 ?? num1;
print("num3:\(num3)")
num2 = 2;
num3 = num2 ?? num1;
print("num3:\(num3)")
执行结果：
num3:1
num3:2
区间操作符(Range Operators)
1.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.
2.The half-open range operator (a..<b) defines a range
that runs from a to b, but does not include b.
直接查看下面例子即可了解使用:
for index in 1...5 {
print("\(index) times 5 is \(index * 5)")
}
for index in 1..<5 {
print("\(index) times 5 is \(index * 5)")
}
执行结果：
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
1 times 5 is 5
2 times 5 is 10
3 times 5 is 15
4 times 5 is 20
3.The closed range operator has an alternate form for ranges that continue as far as possible in one direction—for
example, a range that includes all the elements of an
array, from index 2 to the end of the array. In these
cases, you can omit the value from one side of the range
operator. This kind of range is called a one-sided range
because the operator has a value on only one side.
例子：
let nums = [1, 2, 3, 4]
for num in nums[2...]{
print("num:\(num)");
}
for num in nums[...2]{
print("num:\(num)");
}
执行结果：
num:3
num:4
num:1
num:2
num:3
