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<i class="fa fa-check"></i> <b>1.</b> 欢迎使用 Swift
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<i class="fa fa-check"></i> <b>1.2.</b> Swift 初见
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<i class="fa fa-check"></i> <b>2.</b> Swift 教程
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<i class="fa fa-check"></i> <b>2.1.</b> 基础部分
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<i class="fa fa-check"></i> <b>2.2.</b> 基本操作符
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<i class="fa fa-check"></i> <b>2.3.</b> 字符串和字符
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<i class="fa fa-check"></i> <b>2.4.</b> 集合类型
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<i class="fa fa-check"></i> <b>2.5.</b> 控制流
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<a href="../chapter2/06_Functions.html">
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<i class="fa fa-check"></i> <b>2.6.</b> 函数
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<li class="chapter " data-level="2.7" data-path="chapter2/07_Closures.html">
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<a href="../chapter2/07_Closures.html">
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<i class="fa fa-check"></i> <b>2.7.</b> 闭包
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<a href="../chapter2/08_Enumerations.html">
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<i class="fa fa-check"></i> <b>2.8.</b> 枚举
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</a>
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<li class="chapter " data-level="2.9" data-path="chapter2/09_Classes_and_Structures.html">
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<a href="../chapter2/09_Classes_and_Structures.html">
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<i class="fa fa-check"></i> <b>2.9.</b> 类和结构体
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</a>
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<li class="chapter " data-level="2.10" data-path="chapter2/10_Properties.html">
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<a href="../chapter2/10_Properties.html">
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<i class="fa fa-check"></i> <b>2.10.</b> 属性
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</a>
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<li class="chapter " data-level="2.11" data-path="chapter2/11_Methods.html">
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<a href="../chapter2/11_Methods.html">
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<i class="fa fa-check"></i> <b>2.11.</b> 方法
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</a>
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<li class="chapter " data-level="2.12" data-path="chapter2/12_Subscripts.html">
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<a href="../chapter2/12_Subscripts.html">
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<i class="fa fa-check"></i> <b>2.12.</b> 下标
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</a>
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</li>
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<li class="chapter " data-level="2.13" data-path="chapter2/13_Inheritance.html">
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<a href="../chapter2/13_Inheritance.html">
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<i class="fa fa-check"></i> <b>2.13.</b> 继承
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</a>
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<li class="chapter " data-level="2.14" data-path="chapter2/14_Initialization.html">
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<a href="../chapter2/14_Initialization.html">
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<i class="fa fa-check"></i> <b>2.14.</b> 构造函数
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</a>
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<li class="chapter " data-level="2.15" data-path="chapter2/15_Deinitialization.html">
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<a href="../chapter2/15_Deinitialization.html">
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<i class="fa fa-check"></i> <b>2.15.</b> 析构函数
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</a>
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<li class="chapter " data-level="2.16" data-path="chapter2/16_Automatic_Reference_Counting.html">
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<a href="../chapter2/16_Automatic_Reference_Counting.html">
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<i class="fa fa-check"></i> <b>2.16.</b> 自动引用计数
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</a>
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</li>
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<li class="chapter " data-level="2.17" data-path="chapter2/17_Optional_Chaining.html">
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<a href="../chapter2/17_Optional_Chaining.html">
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<i class="fa fa-check"></i> <b>2.17.</b> 可选链
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</a>
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</li>
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<li class="chapter " data-level="2.18" data-path="chapter2/18_Type_Casting.html">
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<a href="../chapter2/18_Type_Casting.html">
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<i class="fa fa-check"></i> <b>2.18.</b> 类型检查
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</a>
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</li>
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<li class="chapter " data-level="2.19" data-path="chapter2/19_Nested_Types.html">
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<a href="../chapter2/19_Nested_Types.html">
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<i class="fa fa-check"></i> <b>2.19.</b> 嵌套类型
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</a>
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</li>
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<li class="chapter " data-level="2.20" data-path="chapter2/20_Extensions.html">
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<a href="../chapter2/20_Extensions.html">
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<i class="fa fa-check"></i> <b>2.20.</b> 扩展
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</a>
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</li>
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<li class="chapter " data-level="2.21" data-path="chapter2/21_Protocols.html">
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<a href="../chapter2/21_Protocols.html">
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<i class="fa fa-check"></i> <b>2.21.</b> 接口
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</a>
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</li>
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<li class="chapter " data-level="2.22" data-path="chapter2/22_Generics.html">
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<a href="../chapter2/22_Generics.html">
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<i class="fa fa-check"></i> <b>2.22.</b> 泛型
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</a>
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</li>
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<li class="chapter " data-level="2.23" data-path="chapter2/23_Advanced_Operators.html">
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<a href="../chapter2/23_Advanced_Operators.html">
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<i class="fa fa-check"></i> <b>2.23.</b> 高级操作符
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="3" data-path="chapter3/chapter3.html">
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<a href="../chapter3/chapter3.html">
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<i class="fa fa-check"></i> <b>3.</b> 语言参考
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</a>
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<li class="chapter " data-level="3.1" data-path="chapter3/01_About_the_Language_Reference.html">
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<a href="../chapter3/01_About_the_Language_Reference.html">
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<i class="fa fa-check"></i> <b>3.1.</b> 关于语言参考
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</a>
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</li>
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<li class="chapter " data-level="3.2" data-path="chapter3/02_Lexical_Structure.html">
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<a href="../chapter3/02_Lexical_Structure.html">
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<i class="fa fa-check"></i> <b>3.2.</b> 词法结构
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</a>
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<li class="chapter " data-level="3.3" data-path="chapter3/03_Types.html">
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<a href="../chapter3/03_Types.html">
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<i class="fa fa-check"></i> <b>3.3.</b> 类型
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</a>
|
||
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</li>
|
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|
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<li class="chapter " data-level="3.4" data-path="chapter3/04_Expressions.html">
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<a href="../chapter3/04_Expressions.html">
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<i class="fa fa-check"></i> <b>3.4.</b> 表达式
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</a>
|
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|
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|
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|
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<li class="chapter " data-level="3.5" data-path="chapter3/05_Declarations.html">
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<a href="../chapter3/05_Declarations.html">
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<i class="fa fa-check"></i> <b>3.5.</b> 声明
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</a>
|
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|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.6" data-path="chapter3/06_Attributes.html">
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<a href="../chapter3/06_Attributes.html">
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<i class="fa fa-check"></i> <b>3.6.</b> 属性
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</a>
|
||
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.7" data-path="chapter3/07_Patterns.html">
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<a href="../chapter3/07_Patterns.html">
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<i class="fa fa-check"></i> <b>3.7.</b> 模式
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</a>
|
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|
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</li>
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|
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<li class="chapter " data-level="3.8" data-path="chapter3/08_Generic_Parameters_and_Arguments.html">
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<a href="../chapter3/08_Generic_Parameters_and_Arguments.html">
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<i class="fa fa-check"></i> <b>3.8.</b> 泛型参数
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</a>
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</li>
|
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|
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<li class="chapter " data-level="3.9" data-path="chapter3/09_Summary_of_the_Grammar.html">
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<a href="../chapter3/09_Summary_of_the_Grammar.html">
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<i class="fa fa-check"></i> <b>3.9.</b> 语法总结
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</a>
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</li>
|
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<div class="page-inner">
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<section class="normal" id="section-gitbook_19">
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<h1 id="-functions-">函数（Functions）</h1>
|
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<p>函数是用来完成特定任务的独立的代码块。你给一个函数起一个合适的名字，用来标示函数做什么，并且当函数需要执行的时候，这个名字会被“调用”。</p>
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<p>Swift统一的函数语法足够灵活，可以用来表示任何函数，包括从最简单的没有参数名字的C风格函数，到复杂的带局部和外部参数名的Objective-C风格函数。参数可以提供默认值，以简化函数调用。参数也可以即当做传入参数，也当做传出参数，也就是说，一旦函数执行结束，传入的参数值可以被修改。</p>
|
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<p>在Swift中，每个函数都有一种类型，包括函数的参数值类型和返回值类型。你可以把函数类型当做任何其他普通变量类型一样处理，这样就可以更简单地把函数当做别的函数的参数，也可以从其他函数中返回函数。函数的定义可以写在在其他函数定义中，这样可以在嵌套函数范围内实现功能封装。</p>
|
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<h2 id="-">函数的定义与调用</h2>
|
||
<p>当你定义一个函数时，你可以定义一个或多个有名字和类型的值，作为函数的输入（称为参数，parameters），也可以定义某种类型的值作为函数执行结束的输出（称为返回类型）。</p>
|
||
<p>每个函数有个函数名，用来描述函数执行的任务。要使用一个函数时，你用函数名“调用”，并传给它匹配的输入值（称作实参，arguments）。一个函数的实参必须与函数参数表里参数的顺序一致。</p>
|
||
<p>在下面例子中的函数叫做<code>"greetingForPerson"</code>，之所以叫这个名字是因为这个函数用一个人的名字当做输入，并返回给这个人的问候语。为了完成这个任务，你定义一个输入参数-一个叫做<code>personName</code>的<code>String</code>值，和一个包含给这个人问候语的<code>String</code>类型的返回值：</p>
|
||
<pre><code> func sayHello(personName: String) -> String {
|
||
let greeting = "Hello, " + personName + "!"
|
||
return greeting
|
||
}
|
||
</code></pre><p>所有的这些信息汇总起来成为函数的定义，并以<code>func</code>作为前缀。指定函数返回类型时，用返回箭头<code>-></code>（一个连字符后跟一个右尖括号）后跟返回类型的名称的方式来表示。</p>
|
||
<p>该定义描述了函数做什么，它期望接收什么和执行结束时它返回的结果是什么。这样的定义使的函数可以在别的地方以一种清晰的方式被调用：</p>
|
||
<pre><code> println(sayHello("Anna"))
|
||
// prints "Hello, Anna!"
|
||
println(sayHello("Brian"))
|
||
// prints "Hello, Brian!
|
||
</code></pre><p>调用<code>sayHello</code>函数时，在圆括号中传给它一个<code>String</code>类型的实参。因为这个函数返回一个<code>String</code>类型的值，<code>sayHello</code>可以被包含在<code>println</code>的调用中，用来输出这个函数的返回值，正如上面所示。</p>
|
||
<p>在<code>sayHello</code>的函数体中，先定义了一个新的名为<code>greeting</code>的<code>String</code>常量，同时赋值了给<code>personName</code>的一个简单问候消息。然后用<code>return</code>关键字把这个问候返回出去。一旦<code>return greeting</code>被调用，该函数结束它的执行并返回<code>greeting</code>的当前值。</p>
|
||
<p>你可以用不同的输入值多次调用<code>sayHello</code>。上面的例子展示的是用<code>"Anna"</code>和<code>"Brian"</code>调用的结果，该函数分别返回了不同的结果。</p>
|
||
<p>为了简化这个函数的定义，可以将问候消息的创建和返回写成一句：</p>
|
||
<pre><code> func sayHelloAgain(personName: String) -> String {
|
||
return "Hello again, " + personName + "!"
|
||
}
|
||
println(sayHelloAgain("Anna"))
|
||
// prints "Hello again, Anna!
|
||
</code></pre><h2 id="-">函数参数与返回值</h2>
|
||
|
||
|
||
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|
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