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  GeekBand.Swift-下标与操作符 - Zhan's Blog

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          <h1>GeekBand.Swift-下标与操作符</h1>

        <div class="read-more clearfix">
          <span class="date">2016/5/10</span>

          <span>posted in&nbsp;</span>

              <span class="posted-in"><a href='iOS%E5%AD%A6%E4%B9%A0%E7%AC%94%E8%AE%B0.html'>iOS学习笔记</a></span>


          <span class="comments">


              &nbsp;<a  class="ds-thread-count" data-thread-key="14628720930939.html" data-count-type="comments" href="14628720930939.html#ds-thread"></a>

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      <div class="article-content">
      <h2 id="toc_0">下标</h2>

<blockquote>
<p>下标是Swift的一种属性访问方式，可以描述为带参数的计算属性</p>
</blockquote>

<ul>
<li>下标可以用于class、struct、enum</li>
<li>只能定义实例下标，不能定义类型下标</li>
<li>可以定义读写下标或只读下标</li>
<li>下标的索引参数可以是任意类型，可以设计多个参数</li>
<li>一个类型可以提供多个下标的重载版本（参数不同）</li>
</ul>

<pre><code class="language-swift">
class Vector{
    var datas = [Int](count:100,repeatedValue:0);
    subscript(index:Int)-&gt; Int{
        get{
            return datas[index]
        }
        set{
            datas[index]=newValue
        }
    }
}

var datas=Vector()
for i in 0..&lt;10{
   datas[i]=i
}
for i in 0..&lt;10{
    print(datas[i])
}
</code></pre>

<h2 id="toc_1">操作符</h2>

<blockquote>
<p>Swift的操作符在默认情况下与其他程序语言没什么本质差别</p>
</blockquote>

<h3 id="toc_2">重载操作符</h3>

<p>Swift除了标准操作符之外，还可以针对自定义类型重载标准操作符。重载操作符又称为“操作符函数”，本质是一个全局函数。<br/>
可以重载前缀，中缀，后缀操作符。前缀和后缀操作符需要加关键词prefix和postfix。<br/>
也可以通过将参数设置为inout参数，重载复合赋值操作符，如+=,-=。</p>

<pre><code class="language-swift">class Complex{
    var real=0.0
    var imag=0.0

    init(real:Double, imag:Double){
        self.real=real
        self.imag=imag
    }
}

//中缀操作符
func + (left: Complex, right: Complex) -&gt; Complex {

    return Complex(real: left.real + right.real,
        imag: left.imag + right.imag)
}

var c1=Complex(real: 10,imag: 20)
var c2=Complex(real: 100,imag: 200)
var c3=c1+c2


//前缀操作符
prefix func - (data: Complex) -&gt; Complex {
    return Complex(real: -data.real, imag: -data.imag)
}


var c4 = -c3

//复合赋值操作符
func += (inout left: Complex, right: Complex) {
    left = left + right
}

c1+=c2

//自定义操作符
prefix operator +++ {}

prefix func +++ (inout data: Complex) -&gt; Complex {
    data += data
    return data
}

</code></pre>

<h3 id="toc_3">相等操作符</h3>

<ul>
<li>引用相等(判断对象地址是否相等，仅针对引用类型，不适用值类型)

<ul>
<li>相等 ===</li>
<li>不等 !==</li>
</ul></li>
<li>值相等（判断实例值是否相等，自定义类型需要重载提供值比较语义）

<ul>
<li>相等 ==</li>
<li>不等 !=</li>
</ul></li>
</ul>

<pre><code class="language-swift">//值相等操作符
func == (left: Complex, right: Complex) -&gt; Bool {
    return (left.real == right.real) &amp;&amp; (left.imag == right.imag)
}
func != (left: Complex, right: Complex) -&gt; Bool {
    return !(left == right)
}


var c5=c3

print(c1==c5) //值相等
print(c2==c5) //值不等
print(c1===c5) //引用不等
print(c3===c5) //引用相等
print(c3==c5)

</code></pre>

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