Swift之运算符重载示例详解
<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li>引言</li><li>重载双目运算符</li><li>单目运算符</li><li>复合赋值运算符</li><li>等价运算符 ==</li><li>自定义运算符</li><ul class="second_class_ul"><li>自定义后置运算符</li><li>自定义中置运算符</li></ul></ul></div><p class="maodian"></p><h2>引言</h2><p>在C++中, 运算符是可以重载的, Swift也是支持的</p>
<p>注：<code>=</code>和三目运算符<code>a ? b : c</code>不可重载</p>
<p class="maodian"></p><h2>重载双目运算符</h2>
<div class="jb51code"><pre class="brush:cpp;">class Vector {
var x: Double = 0.0
var y: Double = 0.0
var z: Double = 0.0
init(x: Double, y: Double, z: Double) {
self.x = x
self.y = y
self.z = z
}
convenience init() {
self.init(x: 0, y: 0, z: 0)
}
/// Operator '+' declared in type 'Vector' must be 'static'
/// + 是双目运算符，两个参数
static func +(v1: Vector, v2: Vector) -> Vector {
let vector: Vector = Vector()
vector.x = v1.x + v2.x
vector.y = v1.y + v2.y
vector.z = v1.z + v2.z
return vector
}
}</pre></div>
<p class="maodian"></p><h2>单目运算符</h2>
<p>类和结构体也可以实现单目运算符，单目运算符只运算一个值。</p>
<p>运算符出现在值之前为前缀运算符(prefix, 如 -a)，出现在值之后为后缀运算符(postfix, 如a!)。</p>
<div class="jb51code"><pre class="brush:cpp;">struct Coordinate {
var x: Double = 0.0
var y: Double = 0.0
static prefix func +(coordinate: Coordinate) -> Coordinate {
return Coordinate(x: +coordinate.x, y: +coordinate.y)
}
static prefix func -(coordinate: Coordinate) -> Coordinate {
return Coordinate(x: -coordinate.x, y: -coordinate.y)
}
}
func test() {
let p1 = Coordinate(x: 1.0, y: 1.0)
let p2 = Coordinate(x: 2.0, y: 2.0)
print(-p1) // Coordinate(x: -1.0, y: -1.0)
print(+p2) // Coordinate(x: 2.0, y: 2.0)
}</pre></div>
<p class="maodian"></p><h2>复合赋值运算符</h2>
<p>复合赋值运算符是赋值运算符（=）和其他运算符进行结合, 如 +=、-=</p>
<div class="jb51code"><pre class="brush:cpp;">struct Coordinate {
var x: Double = 0.0
var y: Double = 0.0
// 如果放在全局函数里, 不需要加static, 否则, static不可省略
static func +=(left: inout Coordinate, right: Coordinate) {
left = Coordinate(x: left.x + right.x, y: left.y + right.y)
}
static func -=(c1: inout Coordinate, c2: Coordinate) {
left = Coordinate(x: left.x - right.x , y: left.y - right.y)
}
}
func test() {
var p1 = Coordinate(x: 1.0, y: 1.0)
let p2 = Coordinate(x: 2.0, y: 2.0)
p1 += p2
print(p1) // Coordinate(x: 3.0, y: 3.0)
}</pre></div>
<p class="maodian"></p><h2>等价运算符 ==</h2>
<p>自定义类和结构体没有对等价运算符进行默认的实现。等价运算符一般被称为相等运算符<code>==</code>和不等运算符 <code>!=</code></p>
<div class="jb51code"><pre class="brush:cpp;">struct Coordinate {
var x: Double = 0.0
var y: Double = 0.0
static func ==(c1: Coordinate, c2: Coordinate) -> Bool {
return c1.x == c2.x && c1.y == c2.y
}
static func !=(left: Coordinate, right: Coordinate) -> Bool {
return left.x != right.x || left.y != right.y
}
}
func test() {
let p1 = Coordinate(x: 1.0, y: 1.0)
var p2 = Coordinate(x: 2.0, y: 2.0)
print(p1 == p2) // false
p2.x -= 1
p2.y -= 1
print(p1 == p2) // true
}</pre></div>
<p class="maodian"></p><h2>自定义运算符</h2>
<p>可以自定义前置运算符prefix、后置运算符postfix、中置运算符infix, 约束条件：</p>
<ul><li>只能使用如下字符：<br /><code>- + * / = % < > ! & | ^ . ~</code></li><li>只有中置运算符可以继承优先级组 precdence(后面介绍)</li><li>自定义运算符不可放在类中，必须放在文件作用域中</li></ul>
<p class="maodian"></p><h3>自定义后置运算符</h3>
<div class="jb51code"><pre class="brush:cpp;">struct Coordinate {
var x: Double = 0.0
var y: Double = 0.0
}
// 文件作用域，即全局作用域，不可在class下
prefix operator +++
prefix func +++(coordinate: inout Coordinate) -> Coordinate {
coordinate.x = coordinate.x + coordinate.x
coordinate.y = coordinate.y + coordinate.y
return coordinate
}
func test() {
var p1 = Coordinate(x: 1.0, y: 1.0)
print(+++p1) // Coordinate(x: 2.0, y: 2.0)
}</pre></div>
<p>自定义前置运算符和自定义后置运算符类似</p>
<div class="jb51code"><pre class="brush:cpp;">postfix operator +++
postfix func +++(coordinate: inout Coordinate) -> Coordinate {
coordinate.x = coordinate.x + coordinate.x
coordinate.y = coordinate.y + coordinate.y
return coordinate
}</pre></div>
<p class="maodian"></p><h3>自定义中置运算符</h3>
<div class="jb51code"><pre class="brush:cpp;">precedencegroup MyPrecedence {
// higherThan: AdditionPrecedence // 优先级, 比加法运算高
lowerThan: AdditionPrecedence // 优先级, 比加法运算低
associativity: none // 结合方向:left, right or none
assignment: false // true代表是赋值运算符,false代表非赋值运算符
}
infix operator +++ : MyPrecedence// 继承 MyPrecedence 优先级组(可选)
func +++(left: Int, right: Int) -> Int {
return (left + right) * 2
}
func test() {
print(3+++2)
}</pre></div>
<p>借助自定义运算符，我们可以浪一浪，定义一个操作符，当有值是使用此值，无值时使用想要的默认值，如下所示：</p>
<div class="jb51code"><pre class="brush:cpp;">postfix operator <<<
postfix func <<<(a: String?) -> String { return a ?? "" }
func test() {
print(getStr()<<<)
}
func getStr() -> String? {
return nil
}</pre></div>
<p>示例</p>
<div class="jb51code"><pre class="brush:cpp;">postfix operator <<<
postfix func <<<(a: String?) -> String { return a ?? "" }
postfix func <<<(a: Int?) -> Int { return a ?? 0 }
postfix func <<<(a: Int8?) -> Int8 { return a ?? 0 }
postfix func <<<(a: Int16?) -> Int16 { return a ?? 0 }
postfix func <<<(a: Int32?) -> Int32 { return a ?? 0 }
postfix func <<<(a: Int64?) -> Int64 { return a ?? 0 }
postfix func <<<(a: UInt?) -> UInt { return a ?? 0 }
postfix func <<<(a: Double?) -> Double { return a ?? 0.0 }
postfix func <<<(a: Float?) -> Float { return a ?? 0.0 }
postfix func <<<(a: ?) -> { return a ?? [] }
postfix func <<<(a: ?) -> { return a ?? [] }
postfix func <<<(a: ?) -> { return a ?? [] }
postfix func <<<(a: ?) -> { return a ?? [:]}
postfix func <<<(a: ?) -> { return a ?? [:] }</pre></div>
<p>以上就是Swift之运算符重载示例详解的详细内容，更多关于Swift运算符重载的资料请关注琼殿技术社区其它相关文章！</p>
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