Swift运算符使用方法浅析
<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li>溢出运算符（Overflow Operator）</li><li>运算符重载（Operator Overload）</li><ul class="second_class_ul"><li>Equatable</li><li>Comparable</li></ul><li>自定义运算符 (Custom Operator)</li><ul class="second_class_ul"></ul></ul></div><p class="maodian"></p><h2>溢出运算符（Overflow Operator）</h2><p>1、Swift的算数运算符出现溢出时会抛出运行时错误</p>
<div class="jb51code"><pre class="brush:java;">var v: UInt8 = UInt8.min
v -= 1</pre></div>
<p>2、Swift有溢出运算符（&+、&-、&*），用来支持溢出运算</p>
<div class="jb51code"><pre class="brush:java;">var v1 = UInt8.min
var v2 = v1 &- 1 //v2 = 255</pre></div>
<div class="jb51code"><pre class="brush:java;">var v1 = UInt8.max
var v2 = v1 &* 2 // 等价于 v1 &+ v1</pre></div>
<p class="maodian"></p><h2>运算符重载（Operator Overload）</h2>
<p>1、类、结构体、枚举可以为现有的运算符提供自定义的实现，这个操作叫做：运算符重载</p>
<div class="jb51code"><pre class="brush:java;">struct Point {
var x = 0, y = 0
static func + (p1: Point, p2: Point) -> Point {
Point(x: p1.x + p2.x, y: p1.y + p2.y)
}
static prefix func - (p: Point) -> Point {
Point(x: -p.x, y: -p.y)
}
static func += (p1: inout Point, p2: Point) {
p1 = p1 + p2
}
static postfix func ++ (p: inout Point) -> Point {
let tmp = p
p += Point(x: 1, y: 1)
return tmp
}
static prefix func ++ (p: inout Point) -> Point {
p += Point(x: 1, y: 1)
return p
}
}
var p1 = Point(x: 10, y: 20)
var p2 = Point(x: 11, y: 22)
let p3 = p1 + p2
let p4 = -p3
print(p4)</pre></div>
<p class="maodian"></p><h3>Equatable</h3>
<p>1、要想得知2个实例是否等价，一般做法是遵守Equatable协议，重载 == 运算符</p>
<p>与此同时，等价于重载了 != 运算符</p>
<div class="jb51code"><pre class="brush:java;">class Person: Equatable {
var age: Int
init(age: Int) {
self.age = age
}
static func == (lhs: Person, rhs: Person) -> Bool {
lhs.age == rhs.age
}
}
var p1 = Person.init(age: 10)
var p2 = Person(age: 11)
print(p1 == p2)</pre></div>
<p>2、Swift为以下类型提供默认的Equatable实现</p>
<p>没有关联类型的枚举</p>
<p>只拥有遵守Equatable协议关联类型的枚举</p>
<p>只拥有遵守Equatable协议存储属性的结构体</p>
<div class="jb51code"><pre class="brush:java;">enum Answer {
case wrong
case right
}
var s1 = Answer.wrong
var s2 = Answer.right
print(s1 == s2)</pre></div>
<p>3、引用类型比较存储的地址值是否相等（是否引用着同一个对象），使用恒等运算符 === 、!==</p>
<p class="maodian"></p><h3>Comparable</h3>
<p>1、要想比较2个实例的大小，一般做法是：遵守Comparable协议，重载相应的运算符</p>
<p class="maodian"></p><h2>自定义运算符 (Custom Operator)</h2>
<p>1、可以自定义新的运算符：在全局作用域使用operator进行声明</p>
<blockquote><p>prefix operator 前缀运算符<br />postfix operator 后缀运算符<br />infix operator 中缀运算符：优先级组</p></blockquote>
<div class="jb51code"><pre class="brush:java;">precedencegroup 优先级组 {
associativity: 结合性(left/right/none)
higherThan: 比谁的优先级高
lowerThan: 比谁的优先级低
assignment: true代表在可选链操作中拥有跟赋值运算符一样的优先级
}</pre></div>
<div class="jb51code"><pre class="brush:java;">prefix operator +++
prefix func +++ (_ i: inout Int) {
i += 2
}
var age = 10
+++age</pre></div>
<div class="jb51code"><pre class="brush:java;">infix operator +-: PlusMinusPrecedence
precedencegroup PlusMinusPrecedence {
associativity: none
higherThan: AdditionPrecedence
lowerThan: MultiplicationPrecedence
assignment: true
}
struct Point {
var x = 0, y = 0
static func +- (p1: Point, p2: Point) -> Point {
Point(x: p1.x + p2.x, y: p1.y - p2.y)
}
}
class Person {
var age = 0
var point: Point = Point()
}
var p: Person? = Person()
p?.point +- Point(x: 10, y: 20)</pre></div>
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