update 02/20

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                         <h1 id="-swift">关于 Swift</h1>
 <p>Swift 是一种新的编程语言，用于编写 iOS 和 OS X 应用程序。Swift 结合了 C 和 Objective-C 的优点并且不受C的兼容性的限制。Swift 使用安全的编程模式并添加了很多新特性，这将使编程更简单，扩展性更强，也更有趣。除此之外，Swift 还支持人见人爱的 Cocoa 和 Cocoa Touch 框架。拥有了这些特性，Swift将重新定义软件开发。</p>

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                         <h1 id="swift-">Swift 初见</h1>
 <p>本页内容包括：</p>

chapter1/chapter1.html

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                         <h1 id="-swift">欢迎使用 Swift</h1>
 <p>在本章中您将了解 Swift 的特性和开发历史，并对 Swift 有一个初步的了解。</p>

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                         <h1 id="-">基础部分</h1>
 <p>Swift 是 iOS 和 OS X 应用开发的一门新语言。然而，如果你有 C 或者 Objective-C 开发经验的话，你会发现 Swift 的很多内容都是你熟悉的。</p>

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                         <h1 id="-">基础运算符</h1>
 <p>运算符是检查, 改变, 合并值的特殊符号或短语. 例如, 加号 <code>+</code> 把计算两个数的和(如 <code>let i = 1 + 2</code>). 复杂些的运行算包括逻辑与<code>&amp;&amp;</code>(如 <code>if enteredDoorCode &amp;&amp; passedRetinaScan</code>), 还有自增运算符 <code>++i</code> 这样让自身加一的便捷运算.</p>

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                         <h1 id="-strings-and-characters-">字符串和字符 (Strings and Characters)</h1>
 <p>本页包含内容：</p>

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                         <h1 id="-functions-">函数（Functions）</h1>
 <p>本页包含内容：</p>

chapter2/07_Closures.html

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                         <h1 id="-">闭包</h1>
 <p>本页内容包含：</p>

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                         <h3 id="-">类和结构体</h3>
 <p>本页包含内容：</p>

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                         <h1 id="-">析构过程</h1>
 <p>在一个类的实例被释放之前，析构函数被立即调用。用关键字deinit来标示析构函数，类似于初始化函数用init来标示。析构函数只适用于类类型。</p>

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                         <h1 id="-">自动引用计数</h1>
 <p>本页包含内容：</p>

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                         <h1 id="optional-chaining">Optional Chaining</h1>
 <p>可选链（Optional Chaining）是一种可以请求和调用属性、方法及子脚本的过程，它的自判断性体现于请求或调用的目标当前可能为空（<code>nil</code>）。如果自判断的目标有值，那么调用就会成功；相反，如果选择的目标为空（<code>nil</code>），则这种调用将返回空（<code>nil</code>）。多次请求或调用可以被链接在一起形成一个链，如果任何一个节点为空（<code>nil</code>）将导致整个链失效。</p>

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                         <h1 id="-type-casting-">类型检查（Type Casting）</h1>
 <p>（ps：为了方便各位检验所以保留了英文，可删。）

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                         <h1 id="-">类型嵌套</h1>
 <p>本页包含内容：</p>

chapter2/20_Extensions.html

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+                    <section class="normal" id="section-gitbook_28">
+                    
+                        <h1 id="-extensions-">扩展（Extensions）</h1>
+<hr>
+<p>本页包含内容：</p>
+<ul>
+<li>扩展语法（Extension Syntax）</li>
+<li>计算属性（Computed Properties）</li>
+<li>构造器（Initializers）</li>
+<li>方法（Methods）</li>
+<li>下标（Subscripts）</li>
+<li>嵌套类型（Nested Types）</li>
+</ul>
+<p><em>扩展</em>就是向一个已有的类、结构体或枚举类型添加新功能（functionality）。这包括在没有权限获取原始源代码的情况下扩展类型的能力（即<em>逆向建模</em>）。扩展和Objective-C中的分类(categories)类似。（不过与Objective-C不同的是，Swift的扩展没有名字。）</p>
+<p>Swift中的扩展可以：</p>
+<ul>
+<li>添加计算属性和计算静态属性</li>
+<li>定义实例方法和类型方法</li>
+<li>提供新的构造器</li>
+<li>定义下标</li>
+<li>定义和使用新的嵌套类型</li>
+<li>使一个已有类型符合某个接口</li>
+</ul>
+<blockquote>
+<p>注意
+如果你定义了一个扩展向一个已有类型添加新功能，那么这个新功能对该类型的所有已有实例中都是可用的，即使它们是在你的这个扩展的前面定义的。</p>
+</blockquote>
+<h2 id="-">扩展语法</h2>
+<p>声明一个扩展使用关键字<code>extension</code>：</p>
+<pre><code class="lang-javascript">extension SomeType{
+    <span class="hljs-comment">// new functionality to add to SomeType goes here</span>
+}
+</code></pre>
+<p>一个扩展可以扩展一个已有类型，使其能够适配一个或多个接口。当这种情况发生时，接口的名字应该完全按照类或结构体的名字的方式进行书写：</p>
+<pre><code class="lang-javascript">extension SomeType: SomeProtocol, AnotherProctocol{
+    <span class="hljs-comment">// implementation of protocol requirments goes here</span>
+}
+</code></pre>
+<p>按照这种方式添加的接口一致性被称之为<strong>给扩展添加接口一致性(Protocal Conformance)</strong></p>
+<h2 id="-">计算属性</h2>
+<p>扩展可以向已有类型添加计算实例属性和计算类型属性。下面的例子向Swift的内建<code>Double</code>类型添加了5个计算实例属性，从而提供与距离单位协作的基本支持。</p>
+<pre><code class="lang-javascript">extension Double{
+    <span class="hljs-keyword">var</span> km: Double { <span class="hljs-keyword">return</span> self * <span class="hljs-number">1</span>_000<span class="hljs-number">.0</span> }
+    <span class="hljs-keyword">var</span> m : Double { <span class="hljs-keyword">return</span> self }
+    <span class="hljs-keyword">var</span> cm: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">100.0</span> }
+    <span class="hljs-keyword">var</span> mm: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">1</span>_000<span class="hljs-number">.0</span> }
+    <span class="hljs-keyword">var</span> ft: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">3.28084</span> }
+}
+<span class="hljs-keyword">let</span> oneInch = <span class="hljs-number">25.4</span>.mm
+println(<span class="hljs-string">"One inch is \(oneInch) meters"</span>)
+<span class="hljs-comment">// prints "One inch is 0.0254 meters"</span>
+<span class="hljs-keyword">let</span> threeFeet = <span class="hljs-number">3.</span>ft
+println(<span class="hljs-string">"Three feet is \(threeFeet) meters"</span>)
+<span class="hljs-comment">// prints "Three feet is 0.914399970739201 meters"</span>
+</code></pre>
+<p>这些计算属性表达的含义是把一个<code>Double</code>型的值看作是某单位下的长度值。即使它们被实现为计算属性，但这些属性仍可以接一个带有dot语法的浮点型字面值，而这恰恰是使用这些浮点型字面量实现距离转换的方式。</p>
+<p>在上述例子中，一个<code>Double</code>型的值<code>1.0</code>被用来表示“1米”。这就是为什么<code>m</code>计算属性返回<code>self</code>——表达式<code>1.m</code>被认为是计算<code>1.0</code>的<code>Double</code>值。</p>
+<p>其它单位则需要一些转换来表示在米下测量的值。1千米等于1,000米，所以<code>km</code>计算属性要把值乘以<code>1_000.00</code>来转化成单位米下的数值。类似地，1米有3.28024英尺，所以<code>ft</code>计算属性要把对应的<code>Double</code>值除以<code>3.28024</code>来实现英尺到米的单位换算。</p>
+<p>这些属性是只读的计算属性，所有从简考虑它们不用<code>get</code>关键字表示。它们的返回值是<code>Double</code>型，而且可以用于所有接受<code>Double</code>的数学计算中：</p>
+<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> aMarathon = <span class="hljs-number">42.</span>km + <span class="hljs-number">195.</span>m
+println(<span class="hljs-string">"A marathon is \(aMarathon) meters long"</span>)
+<span class="hljs-comment">// prints "A marathon is 42495.0 meters long"</span>
+</code></pre>
+<blockquote>
+<p>注意
+扩展可以添加新的计算属性，但是不可以添加存储属性，也不可以向已有属性添加属性观测器(property observers)。</p>
+</blockquote>
+<h2 id="-">构造器</h2>
+<p>扩展可以向已有类型添加新的构造器。这可以让你扩展其它类型，将你自己的定制类型作为构造器参数，或者提供该类型的原始实现中没有包含的额外初始化选项。</p>
+<blockquote>
+<p>注意
+如果你使用扩展向一个值类型添加一个构造器，该构造器向所有的存储属性提供默认值，而且没有定义任何定制构造器（custom initializers），那么对于来自你的扩展构造器中的值类型，你可以调用默认构造器(default initializers)和成员级构造器(memberwise initializers)。
+正如在值类型的构造器授权中描述的，如果你已经把构造器写成值类型原始实现的一部分，上述规则不再适用。</p>
+</blockquote>
+<p>下面的例子定义了一个用于描述几何矩形的定制结构体<code>Rect</code>。这个例子同时定义了两个辅助结构体<code>Size</code>和<code>Point</code>，它们都把<code>0.0</code>作为所有属性的默认值：</p>
+<pre><code class="lang-javascript">struct Size{
+    <span class="hljs-keyword">var</span> width = <span class="hljs-number">0.0</span>, height = <span class="hljs-number">0.0</span>
+}
+struct Point{
+    <span class="hljs-keyword">var</span> x = <span class="hljs-number">0.0</span>, y = <span class="hljs-number">0.0</span>
+}
+struct Rect{
+    <span class="hljs-keyword">var</span> origin = Point()
+    <span class="hljs-keyword">var</span> size = Size()
+}
+</code></pre>
+<p>因为结构体<code>Rect</code>提供了其所有属性的默认值，所以正如默认构造器中描述的，它可以自动接受一个默认的构造器和一个成员级构造器。这些构造器可以用于构造新的<code>Rect</code>实例：</p>
+<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> defaultRect = Rect()
+<span class="hljs-keyword">let</span> memberwiseRect = Rect(origin: Point(x: <span class="hljs-number">2.0</span>, y: <span class="hljs-number">2.0</span>), 
+    size: Size(width: <span class="hljs-number">5.0</span>, height: <span class="hljs-number">5.0</span>))
+</code></pre>
+<p>你可以提供一个额外的使用特殊中心点和大小的构造器来扩展<code>Rect</code>结构体：</p>
+<pre><code class="lang-javascript">extension Rect{
+    init(center: Point, size: Size){
+        <span class="hljs-keyword">let</span> originX = center.x - (size.width / <span class="hljs-number">2</span>)
+        <span class="hljs-keyword">let</span> originY = center.y - (size.height / <span class="hljs-number">2</span>)
+        self.init(origin: Point(x: originX, y: originY), size: size)
+    }
+}
+</code></pre>
+<p>这个新的构造器首先根据提供的<code>center</code>和<code>size</code>值计算一个合适的原点。然后调用该结构体自动的成员构造器<code>init(origin:size:)</code>，该构造器将新的原点和大小存到了合适的属性中：</p>
+<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> centerRect = Rect(center: Point(x: <span class="hljs-number">4.0</span>, y: <span class="hljs-number">4.0</span>),
+    size: Size(width: <span class="hljs-number">3.0</span>, height: <span class="hljs-number">3.0</span>))
+<span class="hljs-comment">// centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0)</span>
+</code></pre>
+<blockquote>
+<p>注意
+如果你使用扩展提供了一个新的构造器，你依旧有责任保证构造过程能够让所有实例完全初始化。</p>
+</blockquote>
+<h2 id="-">方法</h2>
+<p>扩展可以向已有类型添加新的实例方法和类型方法。下面的例子向<code>Int</code>类型添加一个名为<code>repetitions</code>的新实例方法：</p>
+<pre><code class="lang-javascript">extension Int{
+    func repetitions(task: () -&gt; ()){
+        <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0.</span>.self{
+            task()
+        }
+    }
+}
+</code></pre>
+<p>这个<code>repetitions</code>方法使用了一个<code>() -&gt; ()</code>类型的单参数（single argument），表明函数没有参数而且没有返回值。</p>
+<p>定义该扩展之后，你就可以对任意整数调用<code>repetitions</code>方法,实现的功能则是多次执行某任务：</p>
+<pre><code class="lang-javascript"><span class="hljs-number">3.</span>repetitions({
+    println(<span class="hljs-string">"Hello!"</span>)
+    })
+<span class="hljs-comment">// Hello!</span>
+<span class="hljs-comment">// Hello!</span>
+<span class="hljs-comment">// Hello!</span>
+</code></pre>
+<p>可以使用trailing闭包使调用更加简洁：</p>
+<pre><code class="lang-javascript"><span class="hljs-number">3.</span>repetitions{
+    println(<span class="hljs-string">"Goodbye!"</span>)
+}
+<span class="hljs-comment">// Goodbye!</span>
+<span class="hljs-comment">// Goodbye!</span>
+<span class="hljs-comment">// Goodbye!</span>
+</code></pre>
+<h3 id="-">修改实例方法</h3>
+<p>通过扩展添加的实例方法也可以修改该实例本身。结构体和枚举类型中修改<code>self</code>或其属性的方法必须将该实例方法标注为<code>mutating</code>，正如来自原始实现的修改方法一样。</p>
+<p>下面的例子向Swift的<code>Int</code>类型添加了一个新的名为<code>square</code>的修改方法，来实现一个原始值的平方计算：</p>
+<pre><code class="lang-javascript">extension Int{
+    mutating func square(){
+        self = self * self
+    }
+}
+<span class="hljs-keyword">var</span> someInt = <span class="hljs-number">3</span>
+someInt.square()
+<span class="hljs-comment">// someInt is now 9</span>
+</code></pre>
+<h2 id="-">下标</h2>
+<p>扩展可以向一个已有类型添加新下标。这个例子向Swift内建类型<code>Int</code>添加了一个整型下标。该下标<code>[n]</code>返回十进制数字从右向左数的第n个数字</p>
+<ul>
+<li>123456789[0]返回9</li>
+<li>123456789[1]返回8</li>
+</ul>
+<p>等等</p>
+<pre><code class="lang-javascript">extension Int{
+    subscript(digitIndex: Int) -&gt; Int {
+        <span class="hljs-keyword">var</span> decimalBase = <span class="hljs-number">1</span>
+            <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> <span class="hljs-number">1.</span>..digitIndex{
+                decimalBase *= <span class="hljs-number">10</span>
+            }
+        <span class="hljs-keyword">return</span> (self / decimalBase) % <span class="hljs-number">10</span>
+    }
+}
+<span class="hljs-number">746381295</span>[<span class="hljs-number">0</span>]
+<span class="hljs-comment">// returns 5</span>
+<span class="hljs-number">746381295</span>[<span class="hljs-number">1</span>]
+<span class="hljs-comment">// returns 9</span>
+<span class="hljs-number">746381295</span>[<span class="hljs-number">2</span>]
+<span class="hljs-comment">// returns 2</span>
+<span class="hljs-number">746381295</span>[<span class="hljs-number">8</span>]
+<span class="hljs-comment">// returns 7</span>
+</code></pre>
+<p>如果该<code>Int</code>值没有足够的位数，即下标越界，那么上述实现的下标会返回0，因为它会在数字左边自动补0：</p>
+<pre><code class="lang-javascript"><span class="hljs-number">746381295</span>[<span class="hljs-number">9</span>]
+<span class="hljs-comment">//returns 0, 即等同于：</span>
+<span class="hljs-number">0746381295</span>[<span class="hljs-number">9</span>]
+</code></pre>
+<h2 id="-">嵌套类型</h2>
+<p>扩展可以向已有的类、结构体和枚举添加新的嵌套类型：</p>
+<pre><code class="lang-javascript">extension Character {
+    enum Kind {
+        <span class="hljs-keyword">case</span> Vowel, Consonant, Other
+    }
+    <span class="hljs-keyword">var</span> kind: Kind {
+        <span class="hljs-keyword">switch</span> <span class="hljs-built_in">String</span>(self).lowercaseString {
+        <span class="hljs-keyword">case</span> <span class="hljs-string">"a"</span>, <span class="hljs-string">"e"</span>, <span class="hljs-string">"i"</span>, <span class="hljs-string">"o"</span>, <span class="hljs-string">"u"</span>:
+            <span class="hljs-keyword">return</span> .Vowel
+        <span class="hljs-keyword">case</span> <span class="hljs-string">"b"</span>, <span class="hljs-string">"c"</span>, <span class="hljs-string">"d"</span>, <span class="hljs-string">"f"</span>, <span class="hljs-string">"g"</span>, <span class="hljs-string">"h"</span>, <span class="hljs-string">"j"</span>, <span class="hljs-string">"k"</span>, <span class="hljs-string">"l"</span>, <span class="hljs-string">"m"</span>,
+             <span class="hljs-string">"n"</span>, <span class="hljs-string">"p"</span>, <span class="hljs-string">"q"</span>, <span class="hljs-string">"r"</span>, <span class="hljs-string">"s"</span>, <span class="hljs-string">"t"</span>, <span class="hljs-string">"v"</span>, <span class="hljs-string">"w"</span>, <span class="hljs-string">"x"</span>, <span class="hljs-string">"y"</span>, <span class="hljs-string">"z"</span>:
+            <span class="hljs-keyword">return</span> .Consonant
+        <span class="hljs-keyword">default</span>:
+            <span class="hljs-keyword">return</span> .Other
+        }
+    }
+}
+</code></pre>
+<p>该例子向<code>Character</code>添加了新的嵌套枚举。这个名为<code>Kind</code>的枚举表示特定字符的类型。具体来说，就是表示一个标准的拉丁脚本中的字符是元音还是辅音（不考虑口语和地方变种），或者是其它类型。</p>
+<p>这个类子还向<code>Character</code>添加了一个新的计算实例属性，即<code>kind</code>，用来返回合适的<code>Kind</code>枚举成员。</p>
+<p>现在，这个嵌套枚举可以和一个<code>Character</code>值联合使用了：</p>
+<pre><code class="lang-javascript">func printLetterKinds(word: <span class="hljs-built_in">String</span>) {
+    println(<span class="hljs-string">"'\\(word)' is made up of the following kinds   of letters:"</span>)
+    <span class="hljs-keyword">for</span> character <span class="hljs-keyword">in</span> word {
+        <span class="hljs-keyword">switch</span> character.kind {
+        <span class="hljs-keyword">case</span> .Vowel:
+            print(<span class="hljs-string">"vowel "</span>)
+        <span class="hljs-keyword">case</span> .Consonant:
+            print(<span class="hljs-string">"consonant "</span>)
+        <span class="hljs-keyword">case</span> .Other:
+            print(<span class="hljs-string">"other "</span>)
+        }
+    }
+    print(<span class="hljs-string">"\n"</span>)
+}
+printLetterKinds(<span class="hljs-string">"Hello"</span>)
+<span class="hljs-comment">// 'Hello' is made up of the following kinds of letters:</span>
+<span class="hljs-comment">// consonant vowel consonant consonant vowel</span>
+</code></pre>
+<p>函数<code>printLetterKinds</code>的输入是一个<code>String</code>值并对其字符进行迭代。在每次迭代过程中，考虑当前字符的<code>kind</code>计算属性，并打印出合适的类别描述。所以<code>printLetterKinds</code>就可以用来打印一个完整单词中所有字母的类型，正如上述单词<code>&quot;hello&quot;</code>所展示的。</p>
+<blockquote>
+<p>注意
+由于已知<code>character.kind</code>是<code>Character.Kind</code>型，所以<code>Character.Kind</code>中的所有成员值都可以使用<code>switch</code>语句里的形式简写，比如使用 <code>.Vowel</code>代替<code>Character.Kind.Vowel</code></p>
+</blockquote>
+
+                    
+                    </section>
+                
                 </div>
             </div>
         </div>

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                         <h1 id="-">泛型</h1>
 <hr>

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                         <h1 id="swift-">Swift 教程</h1>
 <p>本章介绍了 Swift 的各种特性及其使用方法，是全书的核心部分。</p>

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                         <h1 id="-">关于语言附注</h1>
 <p>本书的这一节描述了Swift编程语言的形式语法。这里描述的语法是为了帮助您更详细的了解该语言，而不是让您直接实现一个解析器或编译器。</p>

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                         <h1 id="swift-">Swift 编程语言</h1>
 <p>Swift 是苹果在 WWDC 2014 上发布的一款全新的编程语言，本书译自苹果官方的 Swift 教程《The Swift Programming Language》。</p>

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